Hello all,
This series is meant to address two issues with the latency tracing.
The first three patches provide a method to trace latencies that
always occurs very close to each other and to differentiate between
them, in spite of the fact that the latency tracers always work in
overwrite mode.
[PATCH 1/4] This implement fs notification for preempt/irqsoff. It
makes it possible for userspace to detect when a new latency has
been detected.
[PATCH 2/4] This extends the preemptirq_delay_test module so that
it can be used to generate a burst of closely occurring latencies.
[PATCH 3/4] This adds a user space program to the tools directory
that utilizes the fs notification feature and a randomized algorithm
to print out any of the latencies in a burst with approximately equal
probability.
The last patch is not directly connected but doesn't apply cleanly on
its own:
[PATCH 4/4] This adds the option CONFIG_TRACE_CONSOLE_LATENCY to
decide whether we want to trace prints to the console or not.
best regards,
Viktor Rosendahl
Viktor Rosendahl (4):
ftrace: Implement fs notification for preempt/irqsoff tracers
preemptirq_delay_test: Add the burst feature and a sysfs trigger
Add the latency-collector to tools
ftrace: Add an option for tracing console latencies
include/linux/irqflags.h | 13 +
kernel/printk/printk.c | 5 +-
kernel/trace/Kconfig | 21 +
kernel/trace/preemptirq_delay_test.c | 139 ++-
kernel/trace/trace.c | 31 +-
kernel/trace/trace.h | 5 +
kernel/trace/trace_irqsoff.c | 35 +
tools/Makefile | 14 +-
tools/trace/Makefile | 20 +
tools/trace/latency-collector.c | 1190 ++++++++++++++++++++++++++
10 files changed, 1444 insertions(+), 29 deletions(-)
create mode 100644 tools/trace/Makefile
create mode 100644 tools/trace/latency-collector.c
--
2.17.1
This is a tool that is intended to work around the fact that the
preemptoff, irqsoff, and preemptirqsoff tracers only work in
overwrite mode. The idea is to act randomly in such a way that we
do not systematically lose any latencies, so that if enough testing
is done, all latencies will be captured.
It uses inotify to detect changes to /sys/kernel/debug/tracing/trace.
When a latency is detected, it will either sleep or print
immediately, depending on a function that act as an unfair coin
toss.
If immediate print is chosen, it means that we open
/sys/kernel/debug/tracing/trace and thereby cause a blackout period
that will hide any subsequent latencies.
If sleep is chosen, it means that we wait before opening
/sys/kernel/debug/tracing/trace, by default for 1000 ms, to see if
there is another latency during this period. If there is, then we will
lose the previous latency. The coin will be tossed again with a
different probability, and we will either print the new latency, or
possibly a subsequent one.
The probability for the unfair coin toss is chosen so that there
is equal probability to obtain any of the latencies in a burst.
However, this assumes that we make an assumption of how many
latencies there can be. By default the program assumes that there
are no more than 2 latencies in a burst, the probability of immediate
printout will be:
1/2 and 1
Thus, the probabilty of getting each of the two latencies will be 1/2.
If we ever find that there is more than one latency in a series,
meaning that we reach the probability of 1, then the table will be
expanded to:
1/3, 1/2, and 1
Thus, we assume that there are no more than three latencies and each
with a probability of 1/3 of being captured. If the probability of 1
is reached in the new table, that is we see more than two closely
occurring latencies, then the table will again be extended, and so
on.
On my systems, it seems like this scheme works fairly well, as
long as the latencies we trace are long enough, 100 us seems to be
enough. This userspace program receive the inotify event at the end
of a latency, and it has time until the end of the next latency
to react, that is to open /sys/kernel/debug/tracing/trace. Thus,
if we trace latencies that are >100 us, then we have at least 100 us
to react.
Example output:
root@myhost:~# echo 100 > /sys/kernel/debug/tracing/tracing_thresh
root@myhost:~# echo preemptirqsoff > /sys/kernel/debug/tracing/current_tracer
root@myhost:~# latency-collector -rvv -a 11 &
[1] 4915
root@myhost:~# Running with policy rr and priority 99. Using 3 print threads.
/sys/kernel/debug/tracing/trace will be printed with random delay
Start size of the probability table: 11
Print a message when prob. table table changes size: true
Print a warning when an event has been lost: true
Sleep time is: 1000 ms
Initializing probability table to 11
Thread 4916 runs with policy rr and priority 99
Thread 4917 runs with policy rr and priority 99
Thread 4918 runs with policy rr and priority 99
Thread 4919 runs with policy rr and priority 99
root@myhost:~# modprobe preemptirq_delay_test delay=105 test_mode=alternate burst_size=10
2850.638308 Latency 1 printout skipped due to random delay
2850.638383 Latency 2 printout skipped due to random delay
2850.638497 Latency 3 immediate print
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> BEGIN <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
alternat-4922 6d... 0us!: execute_preemptirqtest <-preemptirqtest_2
alternat-4922 6d... 106us : execute_preemptirqtest <-preemptirqtest_2
alternat-4922 6d... 106us : tracer_hardirqs_on <-preemptirqtest_2
alternat-4922 6d... 108us : <stack trace>
=> preemptirqtest_2
=> preemptirq_delay_run
=> kthread
=> ret_from_fork
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> END <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
In the example above, we randomly, happened to get the third latency
in a burst burst of 10. If the experiment is repeated enough times,
we will get all 10.
Sometimes, there will be lost latencies, so that we get:
3054.078294 Latency 44 printout skipped due to inotify loop
..or:
3211.957685 Latency 112 printout skipped due to print loop
In my experience, these are not frequent enough to be a problem.
Also, we do not really lose any latency in these cases, it's
more like we get another latency than what was intended by
the design.
Signed-off-by: Viktor Rosendahl <[email protected]>
---
tools/Makefile | 14 +-
tools/trace/Makefile | 20 +
tools/trace/latency-collector.c | 1190 +++++++++++++++++++++++++++++++
3 files changed, 1218 insertions(+), 6 deletions(-)
create mode 100644 tools/trace/Makefile
create mode 100644 tools/trace/latency-collector.c
diff --git a/tools/Makefile b/tools/Makefile
index 77f1aee8ea01..06b7d74cab3f 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -28,6 +28,7 @@ help:
@echo ' spi - spi tools'
@echo ' objtool - an ELF object analysis tool'
@echo ' tmon - thermal monitoring and tuning tool'
+ @echo ' trace - misc tracing tools'
@echo ' turbostat - Intel CPU idle stats and freq reporting tool'
@echo ' usb - USB testing tools'
@echo ' virtio - vhost test module'
@@ -61,7 +62,7 @@ acpi: FORCE
cpupower: FORCE
$(call descend,power/$@)
-cgroup firewire hv guest spi usb virtio vm bpf iio gpio objtool leds wmi pci firmware: FORCE
+cgroup firewire hv guest spi usb virtio vm bpf iio gpio objtool leds wmi pci firmware trace: FORCE
$(call descend,$@)
liblockdep: FORCE
@@ -96,7 +97,7 @@ kvm_stat: FORCE
all: acpi cgroup cpupower gpio hv firewire liblockdep \
perf selftests spi turbostat usb \
virtio vm bpf x86_energy_perf_policy \
- tmon freefall iio objtool kvm_stat wmi pci
+ tmon freefall iio objtool kvm_stat wmi pci trace
acpi_install:
$(call descend,power/$(@:_install=),install)
@@ -104,7 +105,7 @@ acpi_install:
cpupower_install:
$(call descend,power/$(@:_install=),install)
-cgroup_install firewire_install gpio_install hv_install iio_install perf_install spi_install usb_install virtio_install vm_install bpf_install objtool_install wmi_install pci_install:
+cgroup_install firewire_install gpio_install hv_install iio_install perf_install spi_install usb_install virtio_install vm_install bpf_install objtool_install wmi_install pci_install trace_install:
$(call descend,$(@:_install=),install)
liblockdep_install:
@@ -130,7 +131,7 @@ install: acpi_install cgroup_install cpupower_install gpio_install \
perf_install selftests_install turbostat_install usb_install \
virtio_install vm_install bpf_install x86_energy_perf_policy_install \
tmon_install freefall_install objtool_install kvm_stat_install \
- wmi_install pci_install
+ wmi_install pci_install trace_install
acpi_clean:
$(call descend,power/acpi,clean)
@@ -138,7 +139,7 @@ acpi_clean:
cpupower_clean:
$(call descend,power/cpupower,clean)
-cgroup_clean hv_clean firewire_clean spi_clean usb_clean virtio_clean vm_clean wmi_clean bpf_clean iio_clean gpio_clean objtool_clean leds_clean pci_clean firmware_clean:
+cgroup_clean hv_clean firewire_clean spi_clean usb_clean virtio_clean vm_clean wmi_clean bpf_clean iio_clean gpio_clean objtool_clean leds_clean pci_clean firmware_clean trace_clean:
$(call descend,$(@:_clean=),clean)
liblockdep_clean:
@@ -176,6 +177,7 @@ clean: acpi_clean cgroup_clean cpupower_clean hv_clean firewire_clean \
perf_clean selftests_clean turbostat_clean spi_clean usb_clean virtio_clean \
vm_clean bpf_clean iio_clean x86_energy_perf_policy_clean tmon_clean \
freefall_clean build_clean libbpf_clean libsubcmd_clean liblockdep_clean \
- gpio_clean objtool_clean leds_clean wmi_clean pci_clean firmware_clean
+ gpio_clean objtool_clean leds_clean wmi_clean pci_clean firmware_clean \
+ trace_clean
.PHONY: FORCE
diff --git a/tools/trace/Makefile b/tools/trace/Makefile
new file mode 100644
index 000000000000..59cd483ab01f
--- /dev/null
+++ b/tools/trace/Makefile
@@ -0,0 +1,20 @@
+# SPDX-License-Identifier: GPL-2.0
+# Makefile for vm tools
+#
+TARGETS = latency-collector
+CFLAGS = -Wall -Wextra -g -O2
+LDFLAGS = -lpthread
+
+all: $(TARGETS)
+
+%: %.c
+ $(CC) $(CFLAGS) -o $@ $< $(LDFLAGS)
+
+clean:
+ $(RM) latency-collector
+
+sbindir ?= /usr/sbin
+
+install: all
+ install -d $(DESTDIR)$(sbindir)
+ install -m 755 -p $(TARGETS) $(DESTDIR)$(sbindir)
diff --git a/tools/trace/latency-collector.c b/tools/trace/latency-collector.c
new file mode 100644
index 000000000000..80e7cdeb5372
--- /dev/null
+++ b/tools/trace/latency-collector.c
@@ -0,0 +1,1190 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017, 2018, 2019 BMW Car IT GmbH
+ */
+
+#define _GNU_SOURCE
+#define _POSIX_C_SOURCE 200809L
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <sched.h>
+#include <linux/unistd.h>
+#include <sys/inotify.h>
+#include <unistd.h>
+#include <pthread.h>
+
+static const char *prg_name;
+static const char *prg_unknown = "unknown program name";
+
+static int fd_stdout;
+
+/* These are default values */
+static int sched_policy;
+static bool sched_policy_set;
+
+static int sched_pri;
+static bool sched_pri_set;
+
+static bool trace_enable = true;
+static bool use_random_sleep;
+
+static char inotify_buffer[655360];
+
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+#define bool2str(x) (x ? "true":"false")
+
+#define DEFAULT_NR_PRINTER_THREADS (3)
+static unsigned int nr_threads = DEFAULT_NR_PRINTER_THREADS;
+
+#define DEFAULT_TABLE_SIZE (2)
+static unsigned int table_startsize = DEFAULT_TABLE_SIZE;
+
+static int verbosity;
+
+#define verbose_sizechange() (verbosity >= 1)
+#define verbose_lostevent() (verbosity >= 2)
+
+static const char *debug_tracefile;
+static const char *debug_tracefile_dflt = "/sys/kernel/debug/tracing/trace";
+
+#define DEV_URANDOM "/dev/urandom"
+#define RT_DEFAULT_PRI (99)
+
+#define USEC_PER_MSEC (1000L)
+#define NSEC_PER_USEC (1000L)
+#define NSEC_PER_MSEC (USEC_PER_MSEC * NSEC_PER_USEC)
+
+#define MSEC_PER_SEC (1000L)
+#define USEC_PER_SEC (USEC_PER_MSEC * MSEC_PER_SEC)
+#define NSEC_PER_SEC (NSEC_PER_MSEC * MSEC_PER_SEC)
+
+#define SLEEP_TIME_MS_DEFAULT (1000L)
+
+static long sleep_time = (USEC_PER_MSEC * SLEEP_TIME_MS_DEFAULT);
+
+static char queue_full_warning[] =
+"Could not queue trace for printing. It is likely that events happen faster\n"
+"than what they can be printed. Probably partly because of random sleeping\n";
+
+
+struct policy {
+ const char *name;
+ int policy;
+ int default_pri;
+};
+
+static const struct policy policies[] = {
+ { "other", SCHED_OTHER, 0 },
+ { "batch", SCHED_BATCH, 0 },
+ { "idle", SCHED_IDLE, 0 },
+ { "rr", SCHED_RR, RT_DEFAULT_PRI },
+ { "fifo", SCHED_FIFO, RT_DEFAULT_PRI },
+ { NULL, 0, 0 }
+};
+
+struct entry {
+ int ticket;
+ int ticket_completed_ref;
+};
+
+struct print_state {
+ int ticket_counter;
+ int ticket_completed;
+ pthread_mutex_t mutex;
+ pthread_cond_t cond;
+ int cnt;
+ pthread_mutex_t cnt_mutex;
+};
+
+struct short_msg {
+ char buf[160];
+ int len;
+};
+
+static struct print_state printstate;
+
+#define PROB_TABLE_MAX_SIZE (1000)
+
+int probabilities[PROB_TABLE_MAX_SIZE];
+
+struct sleep_table {
+ int *table;
+ int size;
+ pthread_mutex_t mutex;
+};
+
+static struct sleep_table sleeptable;
+
+#define QUEUE_SIZE (10)
+
+struct queue {
+ struct entry entries[QUEUE_SIZE];
+ int next_prod_idx;
+ int next_cons_idx;
+ pthread_mutex_t mutex;
+ pthread_cond_t cond;
+};
+
+#define MAX_THREADS (40)
+
+struct queue printqueue;
+pthread_t printthread[MAX_THREADS];
+pthread_mutex_t print_mtx = PTHREAD_MUTEX_INITIALIZER;
+#define PRINT_BUFFER_SIZE (1024 * 1024)
+
+static __always_inline void *malloc_or_die(size_t size)
+{
+ void *ptr = malloc(size);
+
+ if (ptr == NULL)
+ err(0, "malloc() failed");
+ return ptr;
+}
+
+static __always_inline void write_or_die(int fd, const char *buf, size_t count)
+{
+ ssize_t r;
+
+ do {
+ r = write(fd, buf, count);
+ if (r < 0) {
+ if (errno == EINTR)
+ continue;
+ err(0, "write() failed");
+ }
+ count -= r;
+ buf += r;
+ } while (count > 0);
+}
+
+static __always_inline void clock_gettime_or_die(clockid_t clk_id,
+ struct timespec *tp)
+{
+ int r = clock_gettime(clk_id, tp);
+
+ if (r != 0)
+ err(0, "clock_gettime() failed");
+}
+
+static void open_stdout(void)
+{
+ if (setvbuf(stdout, NULL, _IONBF, 0) != 0)
+ err(0, "setvbuf() failed");
+ fd_stdout = fileno(stdout);
+ if (fd_stdout < 0)
+ err(0, "fileno() failed");
+}
+
+static __always_inline void get_time_in_future(struct timespec *future,
+ long time_us)
+{
+ long nsec;
+
+ clock_gettime_or_die(CLOCK_MONOTONIC, future);
+ future->tv_sec += time_us / USEC_PER_SEC;
+ nsec = future->tv_nsec + (time_us * NSEC_PER_USEC) % NSEC_PER_SEC;
+ if (nsec >= NSEC_PER_SEC) {
+ future->tv_nsec = nsec % NSEC_PER_SEC;
+ future->tv_sec += 1;
+ }
+}
+
+static __always_inline bool time_has_passed(const struct timespec *time)
+{
+ struct timespec now;
+
+ clock_gettime_or_die(CLOCK_MONOTONIC, &now);
+ if (now.tv_sec > time->tv_sec)
+ return true;
+ if (now.tv_sec < time->tv_sec)
+ return false;
+ return (now.tv_nsec >= time->tv_nsec);
+}
+
+static void init_printstate(void)
+{
+ pthread_condattr_t attr;
+
+ printstate.ticket_counter = 0;
+ printstate.ticket_completed = 0;
+ printstate.cnt = 0;
+
+ if (pthread_mutex_init(&printstate.mutex, NULL) != 0)
+ err(0, "pthread_mutex_init() failed");
+
+ if (pthread_mutex_init(&printstate.cnt_mutex, NULL) != 0)
+ err(0, "pthread_mutex_init() failed");
+
+ if (pthread_condattr_init(&attr) != 0)
+ err(0, "pthread_condattr_init()");
+
+ if (pthread_condattr_setclock(&attr, CLOCK_MONOTONIC) != 0)
+ err(0, "pthread_condattr_setclock()");
+
+ if (pthread_cond_init(&printstate.cond, &attr) != 0)
+ err(0, "pthread_cond_init() failed");
+}
+
+static __always_inline void mutex_lock(pthread_mutex_t *mtx)
+{
+ if (pthread_mutex_lock(mtx) != 0)
+ err(0, "pthread_mutex_lock() failed");
+}
+
+static __always_inline void mutex_unlock(pthread_mutex_t *mtx)
+{
+ if (pthread_mutex_unlock(mtx) != 0)
+ err(0, "pthread_mutex_unlock() failed");
+}
+
+static __always_inline void cond_signal(pthread_cond_t *cond)
+{
+ if (pthread_cond_signal(cond) != 0)
+ err(0, "pthread_cond_signal() failed");
+}
+
+static __always_inline void cond_broadcast(pthread_cond_t *cond)
+{
+ if (pthread_cond_broadcast(cond) != 0)
+ err(0, "pthread_cond_broadcast() failed");
+}
+
+static int printstate_next_ticket(struct entry *req)
+{
+ int r;
+
+ r = ++(printstate.ticket_counter);
+ req->ticket = r;
+ req->ticket_completed_ref = printstate.ticket_completed;
+ cond_broadcast(&printstate.cond);
+ return r;
+}
+
+static __always_inline
+void printstate_mark_req_completed(const struct entry *req)
+{
+ if (req->ticket > printstate.ticket_completed)
+ printstate.ticket_completed = req->ticket;
+}
+
+static __always_inline
+bool printstate_has_new_req_arrived(const struct entry *req)
+{
+ return (printstate.ticket_counter != req->ticket);
+}
+
+static __always_inline int printstate_cnt_inc(void)
+{
+ int value;
+
+ mutex_lock(&printstate.cnt_mutex);
+ value = ++printstate.cnt;
+ mutex_unlock(&printstate.cnt_mutex);
+ return value;
+}
+
+static __always_inline int printstate_cnt_dec(void)
+{
+ int value;
+
+ mutex_lock(&printstate.cnt_mutex);
+ value = --printstate.cnt;
+ mutex_unlock(&printstate.cnt_mutex);
+ return value;
+}
+
+static __always_inline int printstate_cnt_read(void)
+{
+ int value;
+
+ mutex_lock(&printstate.cnt_mutex);
+ value = printstate.cnt;
+ mutex_unlock(&printstate.cnt_mutex);
+ return value;
+}
+
+static __always_inline
+bool prev_req_won_race(const struct entry *req)
+{
+ return (printstate.ticket_completed != req->ticket_completed_ref);
+}
+
+static void sleeptable_resize(int size, bool printout, struct short_msg *msg)
+{
+ int bytes;
+
+ if (printout) {
+ msg->len = 0;
+ if (unlikely(size > PROB_TABLE_MAX_SIZE))
+ bytes = snprintf(msg->buf, sizeof(msg->buf),
+"Cannot increase probability table to %d (maximum size reached)\n", size);
+ else
+ bytes = snprintf(msg->buf, sizeof(msg->buf),
+"Increasing probability table to %d\n", size);
+ if (bytes < 0)
+ warn("snprintf() failed");
+ else
+ msg->len = bytes;
+ }
+
+ if (unlikely(size < 0)) {
+ /* Should never happen */
+ errx(0, "Bad program state at %s:%d", __FILE__, __LINE__);
+ return;
+ }
+ sleeptable.size = size;
+ sleeptable.table = &probabilities[PROB_TABLE_MAX_SIZE - size];
+}
+
+static void init_probabilities(void)
+{
+ int i;
+ int j = 1000;
+
+ for (i = 0; i < PROB_TABLE_MAX_SIZE; i++) {
+ probabilities[i] = 1000 / j;
+ j--;
+ }
+ if (pthread_mutex_init(&sleeptable.mutex, NULL) != 0)
+ err(0, "pthread_mutex_init() failed");
+}
+
+static int table_get_probability(const struct entry *req,
+ struct short_msg *msg)
+{
+ int diff = req->ticket - req->ticket_completed_ref;
+ int rval = 0;
+
+ msg->len = 0;
+ diff--;
+ /* Should never happen...*/
+ if (diff < 0)
+ errx(0, "Programmer assumption error at %s:%d\n", __FILE__,
+ __LINE__);
+ mutex_lock(&sleeptable.mutex);
+ if (diff >= (sleeptable.size - 1)) {
+ rval = sleeptable.table[sleeptable.size - 1];
+ sleeptable_resize(sleeptable.size + 1, verbose_sizechange(),
+ msg);
+ } else {
+ rval = sleeptable.table[diff];
+ }
+ mutex_unlock(&sleeptable.mutex);
+ return rval;
+}
+
+static void init_queue(struct queue *q)
+{
+ q->next_prod_idx = 0;
+ q->next_cons_idx = 0;
+ if (pthread_mutex_init(&q->mutex, NULL) != 0)
+ err(0, "pthread_mutex_init() failed");
+ if (pthread_cond_init(&q->cond, NULL) != 0)
+ err(0, "pthread_cond_init() failed");
+}
+
+static __always_inline int queue_len(const struct queue *q)
+{
+ if (q->next_prod_idx >= q->next_cons_idx)
+ return q->next_prod_idx - q->next_cons_idx;
+ else
+ return QUEUE_SIZE - q->next_cons_idx + q->next_prod_idx;
+}
+
+static __always_inline int queue_nr_free(const struct queue *q)
+{
+ int nr_free = QUEUE_SIZE - queue_len(q);
+
+ /*
+ * If there is only one slot left we will anyway lie and claim that the
+ * queue is full because adding an element will make it appear empty
+ */
+ if (nr_free == 1)
+ nr_free = 0;
+ return nr_free;
+}
+
+static __always_inline void queue_idx_inc(int *idx)
+{
+ *idx = (*idx + 1) % QUEUE_SIZE;
+}
+
+static __always_inline void queue_push_to_back(struct queue *q,
+ const struct entry *e)
+{
+ q->entries[q->next_prod_idx] = *e;
+ queue_idx_inc(&q->next_prod_idx);
+}
+
+static __always_inline struct entry queue_pop_from_front(struct queue *q)
+{
+ struct entry e = q->entries[q->next_cons_idx];
+
+ queue_idx_inc(&q->next_cons_idx);
+ return e;
+}
+
+static __always_inline void queue_cond_signal(struct queue *q)
+{
+ if (pthread_cond_signal(&q->cond) != 0)
+ err(0, "pthread_cond_signal() failed");
+}
+
+static __always_inline void queue_cond_wait(struct queue *q)
+{
+ if (pthread_cond_wait(&q->cond, &q->mutex) != 0)
+ err(0, "pthread_cond_wait() failed");
+}
+
+
+static __always_inline int queue_try_to_add_entry(struct queue *q,
+ const struct entry *e)
+{
+ int r = 0;
+
+ mutex_lock(&q->mutex);
+ if (queue_nr_free(q) > 0) {
+ queue_push_to_back(q, e);
+ cond_signal(&q->cond);
+ } else
+ r = -1;
+ mutex_unlock(&q->mutex);
+ return r;
+}
+
+static struct entry queue_wait_for_entry(struct queue *q)
+{
+ struct entry e;
+
+ mutex_lock(&q->mutex);
+ while (true) {
+ if (queue_len(&printqueue) > 0) {
+ e = queue_pop_from_front(q);
+ break;
+ }
+ queue_cond_wait(q);
+ }
+ mutex_unlock(&q->mutex);
+
+ return e;
+}
+
+static const struct policy *policy_from_name(const char *name)
+{
+ const struct policy *p = &policies[0];
+
+ while (p->name != NULL) {
+ if (!strcmp(name, p->name))
+ return p;
+ p++;
+ }
+ return NULL;
+}
+
+static const char *policy_name(int policy)
+{
+ const struct policy *p = &policies[0];
+ static const char *rval = "unknown";
+
+ while (p->name != NULL) {
+ if (p->policy == policy)
+ return p->name;
+ p++;
+ }
+ return rval;
+}
+
+static bool toss_coin(struct drand48_data *buffer, unsigned int prob)
+{
+ long r;
+
+ if (lrand48_r(buffer, &r) != 0)
+ err(0, "lrand48_r() failed");
+ r = r % 1000L;
+ if (r < prob)
+ return true;
+ else
+ return false;
+}
+
+
+static long go_to_sleep(const struct entry *req)
+{
+ struct timespec future;
+ long delay = sleep_time;
+
+ get_time_in_future(&future, delay);
+
+ mutex_lock(&printstate.mutex);
+ while (!printstate_has_new_req_arrived(req)) {
+ if (pthread_cond_timedwait(&printstate.cond, &printstate.mutex,
+ &future) != 0) {
+ if (errno != ETIMEDOUT && errno != 0)
+ err(0, "pthread_cond_timedwait() %d", errno);
+ }
+ if (time_has_passed(&future))
+ break;
+ };
+
+ if (printstate_has_new_req_arrived(req))
+ delay = -1;
+ mutex_unlock(&printstate.mutex);
+
+ return delay;
+}
+
+
+static void set_priority(void)
+{
+ int r;
+ pid_t pid;
+ struct sched_param param;
+
+ memset(¶m, 0, sizeof(param));
+ param.sched_priority = sched_pri;
+
+ pid = getpid();
+ r = sched_setscheduler(pid, sched_policy, ¶m);
+
+ if (r != 0)
+ err(0, "sched_setscheduler() failed");
+}
+
+pid_t latency_collector_gettid(void)
+{
+ return (pid_t) syscall(__NR_gettid);
+}
+
+static void print_priority(void)
+{
+ pid_t tid;
+ int policy;
+ int r;
+ struct sched_param param;
+
+ tid = latency_collector_gettid();
+ r = pthread_getschedparam(pthread_self(), &policy, ¶m);
+ if (r != 0)
+ err(0, "pthread_getschedparam() failed");
+ mutex_lock(&print_mtx);
+ printf("Thread %d runs with policy %s and priority %d\n", tid,
+ policy_name(policy), param.sched_priority);
+ mutex_unlock(&print_mtx);
+}
+
+static __always_inline
+void __print_skipmessage(const struct short_msg *resize_msg,
+ const struct timespec *timestamp, char *buffer,
+ size_t bufspace, const struct entry *req, bool excuse,
+ const char *str)
+{
+ ssize_t bytes = 0;
+ char *p = &buffer[0];
+ long us, sec;
+ int r;
+
+ sec = timestamp->tv_sec;
+ us = timestamp->tv_nsec / 1000;
+
+ if (resize_msg != NULL && resize_msg->len > 0) {
+ strncpy(p, resize_msg->buf, resize_msg->len);
+ bytes += resize_msg->len;
+ p += resize_msg->len;
+ bufspace -= resize_msg->len;
+ }
+
+ if (excuse)
+ r = snprintf(p, bufspace,
+"%ld.%06ld Latency %d printout skipped due to %s\n",
+ sec, us, req->ticket, str);
+ else
+ r = snprintf(p, bufspace, "%ld.%06ld Latency %d detected\n",
+ sec, us, req->ticket);
+
+ if (r < 0)
+ warn("snprintf() failed");
+ else
+ bytes += r;
+
+ /* These prints could happen concurrently */
+ mutex_lock(&print_mtx);
+ write_or_die(fd_stdout, buffer, bytes);
+ mutex_unlock(&print_mtx);
+}
+
+static void print_skipmessage(const struct short_msg *resize_msg,
+ const struct timespec *timestamp, char *buffer,
+ size_t bufspace, const struct entry *req,
+ bool excuse)
+{
+ __print_skipmessage(resize_msg, timestamp, buffer, bufspace, req,
+ excuse, "random delay");
+}
+
+static void print_lostmessage(const struct timespec *timestamp, char *buffer,
+ size_t bufspace, const struct entry *req,
+ const char *reason)
+{
+ __print_skipmessage(NULL, timestamp, buffer, bufspace, req, true,
+ reason);
+}
+
+static void print_tracefile(const struct short_msg *resize_msg,
+ const struct timespec *timestamp, char *buffer,
+ size_t bufspace, long slept,
+ const struct entry *req)
+{
+ static const int reserve = 256;
+ char *p = &buffer[0];
+ ssize_t bytes = 0;
+ ssize_t bytes_tot = 0;
+ long us, sec;
+ long slept_ms;
+ int trace_fd;
+
+ /* Save some space for the final string and final null char */
+ bufspace = bufspace - reserve - 1;
+
+ if (resize_msg != NULL && resize_msg->len > 0) {
+ bytes = resize_msg->len;
+ strncpy(p, resize_msg->buf, bytes);
+ bytes_tot += bytes;
+ p += bytes;
+ bufspace -= bytes;
+ }
+
+ trace_fd = open(debug_tracefile, O_RDONLY);
+
+ if (trace_fd < 0) {
+ warn("open() failed on %s", debug_tracefile);
+ return;
+ }
+
+ sec = timestamp->tv_sec;
+ us = timestamp->tv_nsec / 1000;
+
+ if (slept != 0) {
+ slept_ms = slept / 1000;
+ bytes = snprintf(p, bufspace,
+"%ld.%06ld Latency %d randomly sleep for %ld ms before print\n",
+ sec, us, req->ticket, slept_ms);
+ } else {
+ bytes = snprintf(p, bufspace,
+ "%ld.%06ld Latency %d immediate print\n", sec,
+ us, req->ticket);
+ }
+
+ if (bytes < 0) {
+ warn("snprintf() failed");
+ return;
+ }
+ p += bytes;
+ bufspace -= bytes;
+ bytes_tot += bytes;
+
+ bytes = snprintf(p, bufspace,
+">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> BEGIN <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<\n"
+ );
+
+ if (bytes < 0) {
+ warn("snprintf() failed");
+ return;
+ }
+
+ p += bytes;
+ bufspace -= bytes;
+ bytes_tot += bytes;
+
+ do {
+ bytes = read(trace_fd, p, bufspace);
+ if (bytes < 0) {
+ if (errno == EINTR)
+ continue;
+ warn("read() failed on %s", debug_tracefile);
+ if (close(trace_fd) != 0)
+ warn("close() failed on %s", debug_tracefile);
+ return;
+ }
+ if (bytes == 0)
+ break;
+ p += bytes;
+ bufspace -= bytes;
+ bytes_tot += bytes;
+ } while (true);
+
+ if (close(trace_fd) != 0)
+ warn("close() failed on %s", debug_tracefile);
+
+ printstate_cnt_dec();
+ /* Add the reserve space back to the budget for the final string */
+ bufspace += reserve;
+
+ bytes = snprintf(p, bufspace,
+ ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> END <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<\n\n");
+
+ if (bytes < 0) {
+ warn("snprintf() failed");
+ return;
+ }
+
+ bytes_tot += bytes;
+
+ /* These prints could happen concurrently */
+ mutex_lock(&print_mtx);
+ write_or_die(fd_stdout, buffer, bytes_tot);
+ mutex_unlock(&print_mtx);
+}
+
+static void do_jittertest(void)
+{
+ int ifd = inotify_init();
+ int wd;
+ const ssize_t bufsize = sizeof(inotify_buffer);
+ const ssize_t istructsize = sizeof(struct inotify_event);
+ char *buf = &inotify_buffer[0];
+ ssize_t nr_read;
+ char *p;
+ int modified;
+ struct inotify_event *event;
+ struct entry req;
+ char *buffer;
+ const size_t bufspace = PRINT_BUFFER_SIZE;
+ struct timespec timestamp;
+
+ print_priority();
+
+ buffer = malloc_or_die(bufspace);
+
+ if (ifd < 0)
+ err(0, "inotify_init() failed!");
+
+ wd = inotify_add_watch(ifd, debug_tracefile, IN_MODIFY);
+ if (wd < 0)
+ err(0, "inotify_add_watch() failed!");
+
+ while (true) {
+ modified = 0;
+ nr_read = read(ifd, buf, bufsize);
+ if (nr_read <= 0)
+ err(0, "read() failed on inotify fd!");
+ if (nr_read == bufsize)
+ warnx("inotify() buffer filled, skipping events");
+ if (nr_read < istructsize)
+ errx(0, "read() returned too few bytes on inotify fd");
+
+ for (p = buf; p < buf + nr_read;) {
+ event = (struct inotify_event *) p;
+ if ((event->mask & IN_MODIFY) != 0)
+ modified++;
+ p += istructsize + event->len;
+ }
+ while (modified > 0) {
+ mutex_lock(&printstate.mutex);
+ printstate_next_ticket(&req);
+ if (printstate_cnt_read() > 0) {
+ printstate_mark_req_completed(&req);
+ mutex_unlock(&printstate.mutex);
+ if (verbose_lostevent()) {
+ clock_gettime_or_die(CLOCK_MONOTONIC,
+ ×tamp);
+ print_lostmessage(×tamp, buffer,
+ bufspace, &req,
+ "inotify loop");
+ }
+ break;
+ }
+ mutex_unlock(&printstate.mutex);
+ if (queue_try_to_add_entry(&printqueue, &req) != 0) {
+ /* These prints could happen concurrently */
+ mutex_lock(&print_mtx);
+ write_or_die(fd_stdout, queue_full_warning,
+ sizeof(queue_full_warning));
+ mutex_unlock(&print_mtx);
+ }
+ modified--;
+ }
+ }
+}
+
+static void *do_printloop(void *arg)
+{
+ const size_t bufspace = PRINT_BUFFER_SIZE;
+ char *buffer;
+ long *rseed = (long *) arg;
+ struct drand48_data drandbuf;
+ long slept = 0;
+ struct entry req;
+ int prob = 0;
+ struct timespec timestamp;
+ struct short_msg resize_msg;
+
+ print_priority();
+
+ if (srand48_r(*rseed, &drandbuf) != 0)
+ err(0, "srand48_r() failed!\n");
+
+ buffer = malloc_or_die(bufspace);
+
+ while (true) {
+ req = queue_wait_for_entry(&printqueue);
+ clock_gettime_or_die(CLOCK_MONOTONIC, ×tamp);
+ mutex_lock(&printstate.mutex);
+ if (prev_req_won_race(&req)) {
+ printstate_mark_req_completed(&req);
+ mutex_unlock(&printstate.mutex);
+ if (verbose_lostevent())
+ print_lostmessage(×tamp, buffer, bufspace,
+ &req, "print loop");
+ continue;
+ }
+ mutex_unlock(&printstate.mutex);
+
+ /*
+ * Toss a coin to decide if we want to sleep a random amount
+ * before printing out the backtrace. The reason for this is
+ * that opening /sys/kernel/debug/tracing/trace will cause a
+ * blackout of about 430 ms, where no latencies will be noted
+ * by the latency tracer. Thus by randomly sleeping a random
+ * amount we try to avoid missing traces systematically due to
+ * this. With this option we will sometimes get the first
+ * latency, some other times some of the later ones, in case of
+ * closely spaced traces.
+ */
+ if (trace_enable && use_random_sleep) {
+ slept = 0;
+ prob = table_get_probability(&req, &resize_msg);
+ if (!toss_coin(&drandbuf, prob))
+ slept = go_to_sleep(&req);
+ if (slept >= 0) {
+ /* A print is ongoing */
+ printstate_cnt_inc();
+ /*
+ * We will do the printout below so we have to
+ * mark it as completed while we still have the
+ * mutex.
+ */
+ mutex_lock(&printstate.mutex);
+ printstate_mark_req_completed(&req);
+ mutex_unlock(&printstate.mutex);
+ }
+ }
+ if (trace_enable) {
+ /*
+ * slept < 0 means that we detected another
+ * notification in go_to_sleep() above
+ */
+ if (slept >= 0)
+ /*
+ * N.B. printstate_cnt_dec(); will be called
+ * inside print_tracefile()
+ */
+ print_tracefile(&resize_msg, ×tamp, buffer,
+ bufspace, slept, &req);
+ else
+ print_skipmessage(&resize_msg, ×tamp,
+ buffer, bufspace, &req, true);
+ } else {
+ print_skipmessage(&resize_msg, ×tamp, buffer,
+ bufspace, &req, false);
+ }
+ }
+ return NULL;
+}
+
+static void start_printthread(void)
+{
+ unsigned int i;
+ long *seed;
+ int ufd;
+
+ ufd = open(DEV_URANDOM, O_RDONLY);
+ if (nr_threads > MAX_THREADS) {
+ warnx(
+"Number of requested print threads was %d, max number is %d\n",
+ nr_threads, MAX_THREADS);
+ nr_threads = MAX_THREADS;
+ }
+ for (i = 0; i < nr_threads; i++) {
+ seed = malloc_or_die(sizeof(*seed));
+ if (ufd < 0 ||
+ read(ufd, seed, sizeof(*seed)) != sizeof(*seed)) {
+ printf(
+"Warning! Using trivial random nummer seed, since %s not available\n",
+ DEV_URANDOM);
+ fflush(stdout);
+ *seed = i;
+ }
+ if (pthread_create(&printthread[i], NULL, do_printloop, seed)
+ != 0)
+ err(0, "pthread_create()");
+ }
+ if (ufd > 0)
+ close(ufd);
+}
+
+static void show_usage(void)
+{
+ printf(
+"Usage: %s [OPTION]...\n\n"
+"Collect closely occurring latencies from %s\n"
+"when any of the following tracers are enabled: preemptirqsoff, preemptoff, or\n"
+"irqsoff. A tracer can be enabled by doing something like this:\n\n"
+
+"echo 1000 > /sys/kernel/debug/tracing/tracing_thresh\n"
+"echo preemptirqsoff > /sys/kernel/debug/tracing/current_tracer\n\n"
+
+"CONFIG_PREEMPTIRQ_FSNOTIFY must be enabled in the kernel configuration.\n\n"
+
+"The following options are supported:\n"
+"-c, --policy POL\tRun the program with scheduling policy POL. POL can be\n"
+"\t\t\tother, batch, idle, rr or fifo.\n\n"
+
+"-p, --priority PRI\tRun the program with priority PRI. The acceptable range\n"
+"\t\t\tof PRI depends on the scheduling policy.\n\n"
+
+"-n, --notrace\t\tIf latency is detected, do not print out the content of\n"
+"\t\t\tthe trace file to standard output\n\n"
+
+"-t, --threads NRTHR\tRun NRTHR threads for printing. Default is %d.\n\n"
+
+"-r, --random\t\tArbitrarily sleep a certain amount of time, default\n"
+"\t\t\t%ld ms, before reading the trace file. The\n"
+"\t\t\tprobabilities for sleep are chosen so that\n"
+"\t\t\tthe probability of obtaining any of a cluster of closely\n"
+"\t\t\toccurring latencies are equal, i.e. we will randomly\n"
+"\t\t\tchoose which one we collect from the trace file.\n\n"
+
+"-a, --nrlat NRLAT\tFor the purpose of arbitrary delay, assume that there\n"
+"\t\t\tare no more than NRLAT clustered latencies. If NRLAT\n"
+"\t\t\tlatencies are detected during a run, this value will\n"
+"\t\t\tautomatically be increased to NRLAT + 1 and then to\n"
+"\t\t\tNRLAT + 2 and so on. The default is %d. This option\n"
+"\t\t\timplies -r. We need to know this number in order to\n"
+"\t\t\tbe able to calculate the probabilities of sleeping.\n"
+"\t\t\tSpecifically, the probabilities of not sleeping, i.e. to\n"
+"\t\t\tdo an immediate printout will be:\n\n"
+"\t\t\t1/NRLAT 1/(NRLAT - 1) ... 1/3 1/2 1\n\n"
+"\t\t\tThe probability of sleeping will be:\n\n"
+"\t\t\t1 - P, where P is from the series above\n\n"
+"\t\t\tThis descending probability will cause us to choose\n"
+"\t\t\tan occurrence at random. Observe that the final\n"
+"\t\t\tprobability is 0, it is when we reach this probability\n"
+"\t\t\tthat we increase NRLAT automatically. As an example,\n"
+"\t\t\twith the default value of 2, the probabilities will be:\n\n"
+"\t\t\t1/2 0\n\n"
+"\t\t\tThis means, when a latency is detected we will sleep\n"
+"\t\t\twith 50%% probability. If we ever detect another latency\n"
+"\t\t\tduring the sleep period, then the probability of sleep\n"
+"\t\t\twill be 0%% and the table will be expanded to:\n\n"
+"\t\t\t1/3 1/2 0\n\n"
+
+"-v, --verbose\t\tIncrease the verbosity. If this option is given once,\n"
+"\t\t\tthen print a message every time that the NRLAT value\n"
+"\t\t\tis automatically increased. If this option is given at\n"
+"\t\t\tleast twice, then also print a warning for lost events.\n\n"
+
+"-u, --time TIME\t\tArbitrarily sleep for a specified time TIME ms before\n"
+"\t\t\tprinting out the trace from the trace file. The default\n"
+"\t\t\tis %ld ms. This option implies -r.\n\n"
+
+"-f, --file FILE\t\tUse FILE as trace file. The default is\n"
+"\t\t\t%s.\n"
+,
+prg_name, debug_tracefile_dflt, DEFAULT_NR_PRINTER_THREADS,
+SLEEP_TIME_MS_DEFAULT, DEFAULT_TABLE_SIZE, SLEEP_TIME_MS_DEFAULT,
+debug_tracefile_dflt);
+}
+
+static void scan_arguments(int argc, char *argv[])
+{
+ int c;
+ int option_idx = 0;
+
+ debug_tracefile = debug_tracefile_dflt;
+
+ static struct option long_options[] = {
+ { "policy", required_argument, 0, 'c' },
+ { "priority", required_argument, 0, 'p' },
+ { "help", no_argument, 0, 'h' },
+ { "notrace", no_argument, 0, 'n' },
+ { "random", no_argument, 0, 'r' },
+ { "nrlat", required_argument, 0, 'a' },
+ { "threads", required_argument, 0, 't' },
+ { "time", required_argument, 0, 'u' },
+ { "verbose", no_argument, 0, 'v' },
+ { "file", required_argument, 0, 'f' },
+ { 0, 0, 0, 0 }
+ };
+ const struct policy *p;
+ int max, min;
+ int value;
+
+ while (true) {
+ c = getopt_long(argc, argv, "c:p:hnra:t:u:vf:", long_options,
+ &option_idx);
+ if (c == -1)
+ break;
+
+ switch (c) {
+ case 'c':
+ p = policy_from_name(optarg);
+ if (p != NULL) {
+ sched_policy = p->policy;
+ sched_policy_set = true;
+ if (!sched_pri_set) {
+ sched_pri = p->default_pri;
+ sched_pri_set = true;
+ }
+ } else {
+ warnx("Unknown scheduling %s\n", optarg);
+ show_usage();
+ exit(0);
+ }
+ break;
+ case 'p':
+ sched_pri = atoi(optarg);
+ sched_pri_set = true;
+ break;
+ case 'h':
+ show_usage();
+ exit(0);
+ break;
+ case 'n':
+ trace_enable = false;
+ use_random_sleep = false;
+ break;
+ case 't':
+ value = atoi(optarg);
+ if (value > 0)
+ nr_threads = value;
+ else {
+ warnx("NRTHR must be > 0\n");
+ show_usage();
+ exit(0);
+ }
+ break;
+ case 'u':
+ value = atoi(optarg);
+ if (value < 0) {
+ warnx("TIME must be >= 0\n");
+ show_usage();
+ exit(0);
+ }
+ trace_enable = true;
+ use_random_sleep = true;
+ sleep_time = value * USEC_PER_MSEC;
+ break;
+ case 'v':
+ verbosity++;
+ break;
+ case 'r':
+ trace_enable = true;
+ use_random_sleep = true;
+ break;
+ case 'a':
+ value = atoi(optarg);
+ if (value <= 0) {
+ warnx("NRLAT must be > 0\n");
+ show_usage();
+ exit(0);
+ }
+ trace_enable = true;
+ use_random_sleep = true;
+ table_startsize = value;
+ break;
+ case 'f':
+ debug_tracefile = strdup(optarg);
+ break;
+ default:
+ show_usage();
+ exit(0);
+ break;
+ }
+ }
+
+ if (!sched_policy_set) {
+ sched_policy = SCHED_RR;
+ sched_policy_set = true;
+ if (!sched_pri_set) {
+ sched_pri = RT_DEFAULT_PRI;
+ sched_pri_set = true;
+ }
+ }
+
+ max = sched_get_priority_max(sched_policy);
+ min = sched_get_priority_min(sched_policy);
+
+ if (sched_pri < min) {
+ printf(
+"ATTENTION: Increasing priority to minimum, which is %d\n", min);
+ sched_pri = min;
+ }
+ if (sched_pri > max) {
+ printf(
+"ATTENTION: Reducing priority to maximum, which is %d\n", max);
+ sched_pri = max;
+ }
+}
+
+static void show_params(void)
+{
+ printf(
+ "Running with policy %s and priority %d. Using %d print threads.\n",
+ policy_name(sched_policy), sched_pri, nr_threads);
+ if (trace_enable) {
+ if (use_random_sleep) {
+ printf(
+"%s will be printed with random delay\n"
+"Start size of the probability table:\t\t\t%d\n"
+"Print a message when prob. table table changes size:\t%s\n"
+"Print a warning when an event has been lost:\t\t%s\n"
+"Sleep time is:\t\t\t\t\t\t%ld ms\n",
+debug_tracefile,
+table_startsize,
+bool2str(verbose_sizechange()),
+bool2str(verbose_lostevent()),
+sleep_time / USEC_PER_MSEC);
+ } else {
+ printf("%s will be printed immedately\n",
+ debug_tracefile);
+ }
+ } else {
+ printf("%s will not be printed\n",
+ debug_tracefile);
+ }
+}
+
+int main(int argc, char *argv[])
+{
+ open_stdout();
+
+ if (argc >= 1)
+ prg_name = argv[0];
+ else
+ prg_name = prg_unknown;
+
+ scan_arguments(argc, argv);
+ show_params();
+
+ init_printstate();
+ init_probabilities();
+ if (verbose_sizechange())
+ printf("Initializing probability table to %d\n",
+ table_startsize);
+ sleeptable_resize(table_startsize, false, NULL);
+ set_priority();
+ init_queue(&printqueue);
+ start_printthread();
+ do_jittertest();
+
+ return 0;
+}
--
2.17.1
This patch implements the feature that the trace file, e.g.
/sys/kernel/debug/tracing/trace will receive notifications through
the fsnotify framework when a new trace is available.
This makes it possible to implement a user space program that can,
with equal probability, obtain traces of latencies that occur
immediately after each other in spite of the fact that the
preempt/irqsoff tracers operate in overwrite mode.
Signed-off-by: Viktor Rosendahl <[email protected]>
---
kernel/trace/Kconfig | 10 ++++++++++
kernel/trace/trace.c | 31 +++++++++++++++++++++++++++++--
kernel/trace/trace.h | 5 +++++
kernel/trace/trace_irqsoff.c | 35 +++++++++++++++++++++++++++++++++++
4 files changed, 79 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index fa8b1fe824f3..ca80cb08bd39 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -234,6 +234,16 @@ config PREEMPT_TRACER
enabled. This option and the irqs-off timing option can be
used together or separately.)
+ config PREEMPTIRQ_FSNOTIFY
+ bool "Generate fsnotify events for the latency tracers"
+ default n
+ depends on (IRQSOFF_TRACER || PREEMPT_TRACER) && FSNOTIFY
+ help
+ This option will enable the generation of fsnotify events for the
+ trace file. This makes it possible for userspace to be notified about
+ modification of /sys/kernel/debug/tracing/trace through the inotify
+ interface.
+
config SCHED_TRACER
bool "Scheduling Latency Tracer"
select GENERIC_TRACER
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c521b7347482..c7db01101ef2 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -44,6 +44,8 @@
#include <linux/trace.h>
#include <linux/sched/clock.h>
#include <linux/sched/rt.h>
+#include <linux/fsnotify.h>
+#include <linux/workqueue.h>
#include "trace.h"
#include "trace_output.h"
@@ -7977,6 +7979,32 @@ static __init void create_trace_instances(struct dentry *d_tracer)
return;
}
+#ifdef CONFIG_PREEMPTIRQ_FSNOTIFY
+
+static void trace_notify_workfn(struct work_struct *work)
+{
+ struct trace_array *tr = container_of(work, struct trace_array,
+ notify_work);
+ fsnotify(tr->d_trace->d_inode, FS_MODIFY, tr->d_trace->d_inode,
+ FSNOTIFY_EVENT_INODE, NULL, 0);
+}
+
+static void trace_create_trace_file(struct trace_array *tr,
+ struct dentry *d_tracer)
+{
+ /* For notify we need to init the work structure and save the pointer */
+ INIT_WORK(&tr->notify_work, trace_notify_workfn);
+ tr->d_trace = trace_create_file("trace", 0644, d_tracer, tr,
+ &tracing_fops);
+}
+
+#else /* !CONFIG_PREEMPTIRQ_FSNOTIFY */
+
+#define trace_create_trace_file(tr, d_tracer) \
+ trace_create_file("trace", 0644, d_tracer, tr, &tracing_fops)
+
+#endif
+
static void
init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
{
@@ -7995,8 +8023,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
trace_create_file("trace_options", 0644, d_tracer,
tr, &tracing_iter_fops);
- trace_create_file("trace", 0644, d_tracer,
- tr, &tracing_fops);
+ trace_create_trace_file(tr, d_tracer);
trace_create_file("trace_pipe", 0444, d_tracer,
tr, &tracing_pipe_fops);
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 08900828d282..a6769438a809 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -17,6 +17,7 @@
#include <linux/compiler.h>
#include <linux/trace_seq.h>
#include <linux/glob.h>
+#include <linux/workqueue.h>
#ifdef CONFIG_FTRACE_SYSCALLS
#include <asm/unistd.h> /* For NR_SYSCALLS */
@@ -257,6 +258,10 @@ struct trace_array {
struct dentry *options;
struct dentry *percpu_dir;
struct dentry *event_dir;
+#ifdef CONFIG_PREEMPTIRQ_FSNOTIFY
+ struct dentry *d_trace;
+ struct work_struct notify_work;
+#endif
struct trace_options *topts;
struct list_head systems;
struct list_head events;
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index d3294721f119..676413504566 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -81,6 +81,31 @@ static inline int irqsoff_display_graph(struct trace_array *tr, int set)
*/
static __cacheline_aligned_in_smp unsigned long max_sequence;
+#ifdef CONFIG_PREEMPTIRQ_FSNOTIFY
+
+static struct workqueue_struct *notify_wq;
+
+static __init void trace_file_notify_init(void)
+{
+ notify_wq = alloc_workqueue("irqsoff_notify_wq",
+ WQ_UNBOUND | WQ_HIGHPRI, 0);
+ if (!notify_wq)
+ pr_err("Unable to allocate irqsoff_notify_wq");
+}
+
+static inline void trace_file_notify(struct trace_array *tr)
+{
+ if (likely(notify_wq))
+ queue_work(notify_wq, &tr->notify_work);
+}
+
+#else /* !CONFIG_PREEMPTIRQ_FSNOTIFY */
+
+#define trace_file_notify_init() do {} while (0)
+#define trace_file_notify(tr) do {} while (0)
+
+#endif /* !CONFIG_PREEMPTIRQ_FSNOTIFY */
+
#ifdef CONFIG_FUNCTION_TRACER
/*
* Prologue for the preempt and irqs off function tracers.
@@ -322,6 +347,7 @@ check_critical_timing(struct trace_array *tr,
u64 T0, T1, delta;
unsigned long flags;
int pc;
+ bool notify = false;
T0 = data->preempt_timestamp;
T1 = ftrace_now(cpu);
@@ -352,6 +378,7 @@ check_critical_timing(struct trace_array *tr,
if (likely(!is_tracing_stopped())) {
tr->max_latency = delta;
update_max_tr_single(tr, current, cpu);
+ notify = true;
}
max_sequence++;
@@ -363,6 +390,13 @@ check_critical_timing(struct trace_array *tr,
data->critical_sequence = max_sequence;
data->preempt_timestamp = ftrace_now(cpu);
__trace_function(tr, CALLER_ADDR0, parent_ip, flags, pc);
+
+ /*
+ * We are optimizing for a high threshold, meaning that this will
+ * happen seldom
+ */
+ if (unlikely(notify))
+ trace_file_notify(tr);
}
static inline void
@@ -740,6 +774,7 @@ static struct tracer preemptirqsoff_tracer __read_mostly =
__init static int init_irqsoff_tracer(void)
{
+ trace_file_notify_init();
#ifdef CONFIG_IRQSOFF_TRACER
register_tracer(&irqsoff_tracer);
#endif
--
2.17.1
This burst feature enables the user to generate a burst of
preempt/irqsoff latencies. This makes it possible to test whether we
are able to detect latencies that systematically occur very close to
each other.
In addition, there is a sysfs trigger, so that it's not necessary to
reload the module to repeat the test. The trigger will appear as
/sys/kernel/preemptirq_delay_test/trigger in sysfs.
Signed-off-by: Viktor Rosendahl <[email protected]>
---
kernel/trace/preemptirq_delay_test.c | 139 +++++++++++++++++++++++----
1 file changed, 120 insertions(+), 19 deletions(-)
diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c
index d8765c952fab..1fc3cdbdd293 100644
--- a/kernel/trace/preemptirq_delay_test.c
+++ b/kernel/trace/preemptirq_delay_test.c
@@ -3,6 +3,7 @@
* Preempt / IRQ disable delay thread to test latency tracers
*
* Copyright (C) 2018 Joel Fernandes (Google) <[email protected]>
+ * Copyright (C) 2018 BMW Car IT GmbH
*/
#include <linux/trace_clock.h>
@@ -10,18 +11,23 @@
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel.h>
+#include <linux/kobject.h>
#include <linux/kthread.h>
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/string.h>
+#include <linux/sysfs.h>
static ulong delay = 100;
-static char test_mode[10] = "irq";
+static char test_mode[12] = "irq";
+static uint burst_size = 1;
-module_param_named(delay, delay, ulong, S_IRUGO);
-module_param_string(test_mode, test_mode, 10, S_IRUGO);
-MODULE_PARM_DESC(delay, "Period in microseconds (100 uS default)");
-MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt or irq (default irq)");
+module_param_named(delay, delay, ulong, 0444);
+module_param_string(test_mode, test_mode, 12, 0444);
+module_param_named(burst_size, burst_size, uint, 0444);
+MODULE_PARM_DESC(delay, "Period in microseconds (100 us default)");
+MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or alternate (default irq)");
+MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
static void busy_wait(ulong time)
{
@@ -34,37 +40,132 @@ static void busy_wait(ulong time)
} while ((end - start) < (time * 1000));
}
-static int preemptirq_delay_run(void *data)
+static __always_inline void irqoff_test(void)
{
unsigned long flags;
+ local_irq_save(flags);
+ busy_wait(delay);
+ local_irq_restore(flags);
+}
+
+static __always_inline void preemptoff_test(void)
+{
+ preempt_disable();
+ busy_wait(delay);
+ preempt_enable();
+}
- if (!strcmp(test_mode, "irq")) {
- local_irq_save(flags);
- busy_wait(delay);
- local_irq_restore(flags);
- } else if (!strcmp(test_mode, "preempt")) {
- preempt_disable();
- busy_wait(delay);
- preempt_enable();
+static void execute_preemptirqtest(int idx)
+{
+ if (!strcmp(test_mode, "irq"))
+ irqoff_test();
+ else if (!strcmp(test_mode, "preempt"))
+ preemptoff_test();
+ else if (!strcmp(test_mode, "alternate")) {
+ if (idx % 2 == 0)
+ irqoff_test();
+ else
+ preemptoff_test();
}
+}
+
+#define DECLARE_TESTFN(POSTFIX) \
+ static void preemptirqtest_##POSTFIX(int idx) \
+ { \
+ execute_preemptirqtest(idx); \
+ } \
+
+DECLARE_TESTFN(0)
+DECLARE_TESTFN(1)
+DECLARE_TESTFN(2)
+DECLARE_TESTFN(3)
+DECLARE_TESTFN(4)
+DECLARE_TESTFN(5)
+DECLARE_TESTFN(6)
+DECLARE_TESTFN(7)
+DECLARE_TESTFN(8)
+DECLARE_TESTFN(9)
+static void (*testfuncs[])(int) = {
+ preemptirqtest_0,
+ preemptirqtest_1,
+ preemptirqtest_2,
+ preemptirqtest_3,
+ preemptirqtest_4,
+ preemptirqtest_5,
+ preemptirqtest_6,
+ preemptirqtest_7,
+ preemptirqtest_8,
+ preemptirqtest_9,
+};
+
+#define NR_TEST_FUNCS ARRAY_SIZE(testfuncs)
+
+static int preemptirq_delay_run(void *data)
+{
+
+ int i;
+
+ for (i = 0; i < burst_size; i++)
+ (testfuncs[i % NR_TEST_FUNCS])(i);
return 0;
}
-static int __init preemptirq_delay_init(void)
+static struct task_struct *preemptirq_start_test(void)
{
char task_name[50];
- struct task_struct *test_task;
snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
+ return kthread_run(preemptirq_delay_run, NULL, task_name);
+}
+
+
+static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr,
+ const char *buf, size_t count)
+{
+ preemptirq_start_test();
+ return count;
+}
+
+static struct kobj_attribute trigger_attribute =
+ __ATTR(trigger, 0200, NULL, trigger_store);
+
+static struct attribute *attrs[] = {
+ &trigger_attribute.attr,
+ NULL,
+};
+
+static struct attribute_group attr_group = {
+ .attrs = attrs,
+};
+
+static struct kobject *preemptirq_delay_kobj;
+
+static int __init preemptirq_delay_init(void)
+{
+ struct task_struct *test_task;
+ int retval;
+
+ test_task = preemptirq_start_test();
+ retval = PTR_ERR_OR_ZERO(test_task);
+ if (retval != 0)
+ return retval;
+
+ preemptirq_delay_kobj = kobject_create_and_add("preemptirq_delay_test",
+ kernel_kobj);
+ if (!preemptirq_delay_kobj)
+ return -ENOMEM;
+
+ retval = sysfs_create_group(preemptirq_delay_kobj, &attr_group);
+ if (retval)
+ kobject_put(preemptirq_delay_kobj);
- test_task = kthread_run(preemptirq_delay_run, NULL, task_name);
- return PTR_ERR_OR_ZERO(test_task);
+ return retval;
}
static void __exit preemptirq_delay_exit(void)
{
- return;
+ kobject_put(preemptirq_delay_kobj);
}
module_init(preemptirq_delay_init)
--
2.17.1
This new option CONFIG_TRACE_CONSOLE_LATENCY will enable the latency
tracers to trace the console latencies. Previously this has always been
implicitely disabled. I guess this is because they are considered
to be well known and unavoidable.
However, for some organizations it may nevertheless be desirable to
trace them. Basically, we want to be able to tell that there are
latencies in the system under test because someone has incorrectly
enabled the serial console.
Signed-off-by: Viktor Rosendahl <[email protected]>
---
include/linux/irqflags.h | 13 +++++++++++++
kernel/printk/printk.c | 5 +++--
kernel/trace/Kconfig | 11 +++++++++++
3 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 21619c92c377..791bee718448 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -73,6 +73,19 @@ do { \
# define start_critical_timings() do { } while (0)
#endif
+#ifdef CONFIG_TRACE_CONSOLE_LATENCY
+
+#define console_stop_critical_timings() do {} while (0)
+#define console_start_critical_timings() do {} while (0)
+
+#else /* !CONFIG_TRACE_CONSOLE_LATENCY */
+
+/* don't trace print latency */
+#define console_stop_critical_timings() stop_critical_timings()
+#define console_start_critical_timings() start_critical_timings()
+
+#endif /* !CONFIG_TRACE_CONSOLE_LATENCY */
+
/*
* Wrap the arch provided IRQ routines to provide appropriate checks.
*/
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index d3d170374ceb..303b8f656009 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2404,9 +2404,10 @@ void console_unlock(void)
*/
console_lock_spinning_enable();
- stop_critical_timings(); /* don't trace print latency */
+ /* don't trace print latency if it's disabled */
+ console_stop_critical_timings();
call_console_drivers(ext_text, ext_len, text, len);
- start_critical_timings();
+ console_start_critical_timings();
if (console_lock_spinning_disable_and_check()) {
printk_safe_exit_irqrestore(flags);
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index ca80cb08bd39..5063b32de66c 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -244,6 +244,17 @@ config PREEMPT_TRACER
modification of /sys/kernel/debug/tracing/trace through the inotify
interface.
+ config TRACE_CONSOLE_LATENCY
+ bool "Do not turn off latency tracing for the console"
+ default n
+ depends on IRQSOFF_TRACER || PREEMPT_TRACER
+ help
+ Some of the console drivers will cause long unavoidable
+ latencies because they are slow and need to print immediately
+ in a serialized manner. Because of this their latencies are not
+ traced by default. This option will change behavior so that
+ they are traced.
+
config SCHED_TRACER
bool "Scheduling Latency Tracer"
select GENERIC_TRACER
--
2.17.1
Hi Viktor,
Could you CC me on the other patches as well, next time? I am quite
interested and recently have worked on the latency tracer.
Some comments below:
On Mon, Jan 21, 2019 at 02:35:11PM +0200, Viktor Rosendahl wrote:
> This burst feature enables the user to generate a burst of
> preempt/irqsoff latencies. This makes it possible to test whether we
> are able to detect latencies that systematically occur very close to
> each other.
>
> In addition, there is a sysfs trigger, so that it's not necessary to
> reload the module to repeat the test. The trigger will appear as
> /sys/kernel/preemptirq_delay_test/trigger in sysfs.
>
> Signed-off-by: Viktor Rosendahl <[email protected]>
> ---
> kernel/trace/preemptirq_delay_test.c | 139 +++++++++++++++++++++++----
> 1 file changed, 120 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/trace/preemptirq_delay_test.c b/kernel/trace/preemptirq_delay_test.c
> index d8765c952fab..1fc3cdbdd293 100644
> --- a/kernel/trace/preemptirq_delay_test.c
> +++ b/kernel/trace/preemptirq_delay_test.c
> @@ -3,6 +3,7 @@
> * Preempt / IRQ disable delay thread to test latency tracers
> *
> * Copyright (C) 2018 Joel Fernandes (Google) <[email protected]>
> + * Copyright (C) 2018 BMW Car IT GmbH
> */
>
> #include <linux/trace_clock.h>
> @@ -10,18 +11,23 @@
> #include <linux/interrupt.h>
> #include <linux/irq.h>
> #include <linux/kernel.h>
> +#include <linux/kobject.h>
> #include <linux/kthread.h>
> #include <linux/module.h>
> #include <linux/printk.h>
> #include <linux/string.h>
> +#include <linux/sysfs.h>
>
> static ulong delay = 100;
> -static char test_mode[10] = "irq";
> +static char test_mode[12] = "irq";
> +static uint burst_size = 1;
>
> -module_param_named(delay, delay, ulong, S_IRUGO);
> -module_param_string(test_mode, test_mode, 10, S_IRUGO);
> -MODULE_PARM_DESC(delay, "Period in microseconds (100 uS default)");
> -MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt or irq (default irq)");
> +module_param_named(delay, delay, ulong, 0444);
> +module_param_string(test_mode, test_mode, 12, 0444);
> +module_param_named(burst_size, burst_size, uint, 0444);
> +MODULE_PARM_DESC(delay, "Period in microseconds (100 us default)");
> +MODULE_PARM_DESC(test_mode, "Mode of the test such as preempt, irq, or alternate (default irq)");
> +MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
Where are we bounds checking the burst_size here? It seems like a high
burst_size can overflow your array of functions.
>
> static void busy_wait(ulong time)
> {
> @@ -34,37 +40,132 @@ static void busy_wait(ulong time)
> } while ((end - start) < (time * 1000));
> }
>
> -static int preemptirq_delay_run(void *data)
> +static __always_inline void irqoff_test(void)
> {
> unsigned long flags;
> + local_irq_save(flags);
> + busy_wait(delay);
> + local_irq_restore(flags);
> +}
> +
> +static __always_inline void preemptoff_test(void)
> +{
> + preempt_disable();
> + busy_wait(delay);
> + preempt_enable();
> +}
>
> - if (!strcmp(test_mode, "irq")) {
> - local_irq_save(flags);
> - busy_wait(delay);
> - local_irq_restore(flags);
> - } else if (!strcmp(test_mode, "preempt")) {
> - preempt_disable();
> - busy_wait(delay);
> - preempt_enable();
> +static void execute_preemptirqtest(int idx)
> +{
> + if (!strcmp(test_mode, "irq"))
> + irqoff_test();
> + else if (!strcmp(test_mode, "preempt"))
> + preemptoff_test();
> + else if (!strcmp(test_mode, "alternate")) {
> + if (idx % 2 == 0)
> + irqoff_test();
> + else
> + preemptoff_test();
> }
> +}
> +
> +#define DECLARE_TESTFN(POSTFIX) \
> + static void preemptirqtest_##POSTFIX(int idx) \
> + { \
> + execute_preemptirqtest(idx); \
> + } \
> +
> +DECLARE_TESTFN(0)
> +DECLARE_TESTFN(1)
> +DECLARE_TESTFN(2)
> +DECLARE_TESTFN(3)
> +DECLARE_TESTFN(4)
> +DECLARE_TESTFN(5)
> +DECLARE_TESTFN(6)
> +DECLARE_TESTFN(7)
> +DECLARE_TESTFN(8)
> +DECLARE_TESTFN(9)
You really only need 2 functions here, since the odd and even suffixed
functions are identical.
> +static void (*testfuncs[])(int) = {
> + preemptirqtest_0,
> + preemptirqtest_1,
> + preemptirqtest_2,
> + preemptirqtest_3,
> + preemptirqtest_4,
> + preemptirqtest_5,
> + preemptirqtest_6,
> + preemptirqtest_7,
> + preemptirqtest_8,
> + preemptirqtest_9,
> +};
And then just have an array of 2 functions. Or nuke the array.
> +#define NR_TEST_FUNCS ARRAY_SIZE(testfuncs)
> +
> +static int preemptirq_delay_run(void *data)
> +{
> +
> + int i;
> +
> + for (i = 0; i < burst_size; i++)
> + (testfuncs[i % NR_TEST_FUNCS])(i);
> return 0;
> }
>
> -static int __init preemptirq_delay_init(void)
> +static struct task_struct *preemptirq_start_test(void)
> {
> char task_name[50];
> - struct task_struct *test_task;
>
> snprintf(task_name, sizeof(task_name), "%s_test", test_mode);
> + return kthread_run(preemptirq_delay_run, NULL, task_name);
> +}
> +
> +
> +static ssize_t trigger_store(struct kobject *kobj, struct kobj_attribute *attr,
> + const char *buf, size_t count)
> +{
> + preemptirq_start_test();
> + return count;
> +}
I honestly feel a sysfs trigger file is pointless. Why can't the module be
reloaded? Note also that module parameters can be changed after the module
has been loaded. Perhaps that can be used as a trigger? So if the test_mode
is changed, then the test is re-run.
However, if Steve prefers the sysfs trigger file, then I am Ok with that.
thanks,
- Joel
Hi Joel,
On Tue, 2019-01-22 at 16:53 -0500, Joel Fernandes wrote:
> Could you CC me on the other patches as well, next time? I am quite
> interested and recently have worked on the latency tracer.
>
Sure, I will.
>
> > +MODULE_PARM_DESC(burst_size, "The size of a burst (default 1)");
>
> Where are we bounds checking the burst_size here? It seems like a high
> burst_size can overflow your array of functions.
>
I don't think so. I use "i % NR_TEST_FUNCS" as index when I call functions in
the array.
Basically, if the user specifies a burst size larger than 10, then we will begin
to reuse the test functions.
> >
> > +DECLARE_TESTFN(9)
>
> You really only need 2 functions here, since the odd and even suffixed
> functions are identical.
>
This would indeed make the code more neat and compact.
However, it would no longer be a good test for the latency-collector, which I
posted here:
https://lkml.org/lkml/2019/1/21/572
If we want to test the latency-collector properly, we need backtraces that look
different from each other, otherwise, there is no way of knowing whether the
latency-collector captured the first latency, the last latency or one somewhere
in the middle.
With my code we see backtraces like this:
=> preemptirqtest_4
=> preemptirq_delay_run
=> kthread
=> ret_from_fork
This tells us that the latency-collector captured the 5th latency in a burst. I
want to be able to see that, yes the latency-collector can fish out the 5th
latency in a burst of 10.
Having 10 testfunctions and then reusing them with the modulo game is an attempt
at a compromise between having an inifinte number of testfunctions and compact
code. An alternative would be to check that the burst_size parameter is not
greater than the number of functions.
> >
>
> I honestly feel a sysfs trigger file is pointless. Why can't the module be
> reloaded?
It is just a convenenince for lazy people who manually want to repeat the same
test without having to write a shell script with modprobe & rmmod. Or perhaps
for those who are worried about spending CPU cycles on module loading :)
> Note also that module parameters can be changed after the module
> has been loaded. Perhaps that can be used as a trigger?
I was not aware of this possibility. I can try to make it so if it's desired.
> So if the test_mode
> is changed, then the test is re-run.
>
> However, if Steve prefers the sysfs trigger file, then I am Ok with that.
>
>
I would still prefer to keep the sysfs trigger but I don't insist on it.
When testing the latency-collector it's often desired to repeat the exact same
test many times.
Thanks for the comments.
best regards,
Viktor