Changelog RFC v4 --> PATCH v5:
1. Added a CPU online check prior to parsing the CPU topology to avoid
parsing topologies for CPUs unavailable for the latency test
2. Added comment describing the selftest in cpuidle.sh
As I have made changes to cpuidle.sh's working, hence dropping
"Reviewed-by" from Doug Smythies for the second patch, while retaining
it for the first patch.
RFC v4: https://lkml.org/lkml/2021/4/12/99
---
A kernel module + userspace driver to estimate the wakeup latency
caused by going into stop states. The motivation behind this program is
to find significant deviations behind advertised latency and residency
values.
The patchset measures latencies for two kinds of events. IPIs and Timers
As this is a software-only mechanism, there will additional latencies of
the kernel-firmware-hardware interactions. To account for that, the
program also measures a baseline latency on a 100 percent loaded CPU
and the latencies achieved must be in view relative to that.
To achieve this, we introduce a kernel module and expose its control
knobs through the debugfs interface that the selftests can engage with.
The kernel module provides the following interfaces within
/sys/kernel/debug/latency_test/ for,
IPI test:
ipi_cpu_dest = Destination CPU for the IPI
ipi_cpu_src = Origin of the IPI
ipi_latency_ns = Measured latency time in ns
Timeout test:
timeout_cpu_src = CPU on which the timer to be queued
timeout_expected_ns = Timer duration
timeout_diff_ns = Difference of actual duration vs expected timer
Sample output on a POWER9 system is as follows:
# --IPI Latency Test---
# Baseline Average IPI latency(ns): 3114
# Observed Average IPI latency(ns) - State0: 3265
# Observed Average IPI latency(ns) - State1: 3507
# Observed Average IPI latency(ns) - State2: 3739
# Observed Average IPI latency(ns) - State3: 3807
# Observed Average IPI latency(ns) - State4: 17070
# Observed Average IPI latency(ns) - State5: 1038174
# Observed Average IPI latency(ns) - State6: 1068784
#
# --Timeout Latency Test--
# Baseline Average timeout diff(ns): 1420
# Observed Average timeout diff(ns) - State0: 1640
# Observed Average timeout diff(ns) - State1: 1764
# Observed Average timeout diff(ns) - State2: 1715
# Observed Average timeout diff(ns) - State3: 1845
# Observed Average timeout diff(ns) - State4: 16581
# Observed Average timeout diff(ns) - State5: 939977
# Observed Average timeout diff(ns) - State6: 1073024
Things to keep in mind:
1. This kernel module + bash driver does not guarantee idleness on a
core when the IPI and the Timer is armed. It only invokes sleep and
hopes that the core is idle once the IPI/Timer is invoked onto it.
Hence this program must be run on a completely idle system for best
results
2. Even on a completely idle system, there maybe book-keeping tasks or
jitter tasks that can run on the core we want idle. This can create
outliers in the latency measurement. Thankfully, these outliers
should be large enough to easily weed them out.
3. A userspace only selftest variant was also sent out as RFC based on
suggestions over the previous patchset to simply the kernel
complexeity. However, a userspace only approach had more noise in
the latency measurement due to userspace-kernel interactions
which led to run to run variance and a lesser accurate test.
Another downside of the nature of a userspace program is that it
takes orders of magnitude longer to complete a full system test
compared to the kernel framework.
RFC patch: https://lkml.org/lkml/2020/9/2/356
4. For Intel Systems, the Timer based latencies don't exactly give out
the measure of idle latencies. This is because of a hardware
optimization mechanism that pre-arms a CPU when a timer is set to
wakeup. That doesn't make this metric useless for Intel systems,
it just means that is measuring IPI/Timer responding latency rather
than idle wakeup latencies.
(Source: https://lkml.org/lkml/2020/9/2/610)
For solution to this problem, a hardware based latency analyzer is
devised by Artem Bityutskiy from Intel.
https://youtu.be/Opk92aQyvt0?t=8266
https://intel.github.io/wult/
Pratik R. Sampat (2):
cpuidle: Extract IPI based and timer based wakeup latency from idle
states
selftest/cpuidle: Add support for cpuidle latency measurement
drivers/cpuidle/Makefile | 1 +
drivers/cpuidle/test-cpuidle_latency.c | 157 ++++++++
lib/Kconfig.debug | 10 +
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/cpuidle/Makefile | 6 +
tools/testing/selftests/cpuidle/cpuidle.sh | 414 +++++++++++++++++++++
tools/testing/selftests/cpuidle/settings | 2 +
7 files changed, 591 insertions(+)
create mode 100644 drivers/cpuidle/test-cpuidle_latency.c
create mode 100644 tools/testing/selftests/cpuidle/Makefile
create mode 100755 tools/testing/selftests/cpuidle/cpuidle.sh
create mode 100644 tools/testing/selftests/cpuidle/settings
--
2.17.1
Introduce a mechanism to fire directed IPIs from a specified source CPU
to a specified target CPU and measure the difference in time incurred on
wakeup.
Also, introduce a mechanism to queue a HR timer on a specified CPU and
subsequently measure the time taken to wakeup the CPU.
Finally define a simple debugfs interface to control the knobs to fire
the IPI and Timer events on specified CPU and view their incurred idle
wakeup latencies.
CC: Rafael J. Wysocki <[email protected]>
CC: Daniel Lezcano <[email protected]>
CC: Shuah Khan <[email protected]>
Signed-off-by: Pratik R. Sampat <[email protected]>
Reviewed-by: Doug Smythies <[email protected]>
---
drivers/cpuidle/Makefile | 1 +
drivers/cpuidle/test-cpuidle_latency.c | 157 +++++++++++++++++++++++++
lib/Kconfig.debug | 10 ++
3 files changed, 168 insertions(+)
create mode 100644 drivers/cpuidle/test-cpuidle_latency.c
diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index 26bbc5e74123..3b4ee06a9164 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o
obj-$(CONFIG_DT_IDLE_STATES) += dt_idle_states.o
obj-$(CONFIG_ARCH_HAS_CPU_RELAX) += poll_state.o
obj-$(CONFIG_HALTPOLL_CPUIDLE) += cpuidle-haltpoll.o
+obj-$(CONFIG_IDLE_LATENCY_SELFTEST) += test-cpuidle_latency.o
##################################################################################
# ARM SoC drivers
diff --git a/drivers/cpuidle/test-cpuidle_latency.c b/drivers/cpuidle/test-cpuidle_latency.c
new file mode 100644
index 000000000000..f138011ac225
--- /dev/null
+++ b/drivers/cpuidle/test-cpuidle_latency.c
@@ -0,0 +1,157 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Module-based API test facility for cpuidle latency using IPIs and timers
+ */
+
+#include <linux/debugfs.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+/*
+ * IPI based wakeup latencies
+ * Measure time taken for a CPU to wakeup on a IPI sent from another CPU
+ * The latency measured also includes the latency of sending the IPI
+ */
+struct latency {
+ unsigned int src_cpu;
+ unsigned int dest_cpu;
+ ktime_t time_start;
+ ktime_t time_end;
+ u64 latency_ns;
+} ipi_wakeup;
+
+static void measure_latency(void *info)
+{
+ struct latency *v;
+ ktime_t time_diff;
+
+ v = (struct latency *)info;
+ v->time_end = ktime_get();
+ time_diff = ktime_sub(v->time_end, v->time_start);
+ v->latency_ns = ktime_to_ns(time_diff);
+}
+
+void run_smp_call_function_test(unsigned int cpu)
+{
+ ipi_wakeup.src_cpu = smp_processor_id();
+ ipi_wakeup.dest_cpu = cpu;
+ ipi_wakeup.time_start = ktime_get();
+ smp_call_function_single(cpu, measure_latency, &ipi_wakeup, 1);
+}
+
+/*
+ * Timer based wakeup latencies
+ * Measure time taken for a CPU to wakeup on a timer being armed and fired
+ */
+struct timer_data {
+ unsigned int src_cpu;
+ u64 timeout;
+ ktime_t time_start;
+ ktime_t time_end;
+ struct hrtimer timer;
+ u64 timeout_diff_ns;
+} timer_wakeup;
+
+static enum hrtimer_restart timer_called(struct hrtimer *hrtimer)
+{
+ struct timer_data *w;
+ ktime_t time_diff;
+
+ w = container_of(hrtimer, struct timer_data, timer);
+ w->time_end = ktime_get();
+
+ time_diff = ktime_sub(w->time_end, w->time_start);
+ time_diff = ktime_sub(time_diff, ns_to_ktime(w->timeout));
+ w->timeout_diff_ns = ktime_to_ns(time_diff);
+ return HRTIMER_NORESTART;
+}
+
+static void run_timer_test(unsigned int ns)
+{
+ hrtimer_init(&timer_wakeup.timer, CLOCK_MONOTONIC,
+ HRTIMER_MODE_REL);
+ timer_wakeup.timer.function = timer_called;
+ timer_wakeup.src_cpu = smp_processor_id();
+ timer_wakeup.timeout = ns;
+ timer_wakeup.time_start = ktime_get();
+
+ hrtimer_start(&timer_wakeup.timer, ns_to_ktime(ns),
+ HRTIMER_MODE_REL_PINNED);
+}
+
+static struct dentry *dir;
+
+static int cpu_read_op(void *data, u64 *dest_cpu)
+{
+ *dest_cpu = ipi_wakeup.dest_cpu;
+ return 0;
+}
+
+static int cpu_write_op(void *data, u64 value)
+{
+ run_smp_call_function_test(value);
+ return 0;
+}
+DEFINE_SIMPLE_ATTRIBUTE(ipi_ops, cpu_read_op, cpu_write_op, "%llu\n");
+
+static int timeout_read_op(void *data, u64 *timeout)
+{
+ *timeout = timer_wakeup.timeout;
+ return 0;
+}
+
+static int timeout_write_op(void *data, u64 value)
+{
+ run_timer_test(value);
+ return 0;
+}
+DEFINE_SIMPLE_ATTRIBUTE(timeout_ops, timeout_read_op, timeout_write_op, "%llu\n");
+
+static int __init latency_init(void)
+{
+ struct dentry *temp;
+
+ dir = debugfs_create_dir("latency_test", 0);
+ if (!dir) {
+ pr_alert("latency_test: failed to create /sys/kernel/debug/latency_test\n");
+ return -1;
+ }
+ temp = debugfs_create_file("ipi_cpu_dest",
+ 0666,
+ dir,
+ NULL,
+ &ipi_ops);
+ if (!temp) {
+ pr_alert("latency_test: failed to create /sys/kernel/debug/ipi_cpu_dest\n");
+ return -1;
+ }
+ debugfs_create_u64("ipi_latency_ns", 0444, dir, &ipi_wakeup.latency_ns);
+ debugfs_create_u32("ipi_cpu_src", 0444, dir, &ipi_wakeup.src_cpu);
+
+ temp = debugfs_create_file("timeout_expected_ns",
+ 0666,
+ dir,
+ NULL,
+ &timeout_ops);
+ if (!temp) {
+ pr_alert("latency_test: failed to create /sys/kernel/debug/timeout_expected_ns\n");
+ return -1;
+ }
+ debugfs_create_u64("timeout_diff_ns", 0444, dir, &timer_wakeup.timeout_diff_ns);
+ debugfs_create_u32("timeout_cpu_src", 0444, dir, &timer_wakeup.src_cpu);
+ pr_info("Latency Test module loaded\n");
+ return 0;
+}
+
+static void __exit latency_cleanup(void)
+{
+ pr_info("Cleaning up Latency Test module.\n");
+ debugfs_remove_recursive(dir);
+}
+
+module_init(latency_init);
+module_exit(latency_cleanup);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("IBM Corporation");
+MODULE_DESCRIPTION("Measuring idle latency for IPIs and Timers");
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 417c3d3e521b..70264687e0c2 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1513,6 +1513,16 @@ config DEBUG_KOBJECT
If you say Y here, some extra kobject debugging messages will be sent
to the syslog.
+config IDLE_LATENCY_SELFTEST
+ tristate "Cpuidle latency selftests"
+ depends on CPU_IDLE
+ help
+ This option provides a kernel module that runs tests using the IPI and
+ timers to measure latency.
+
+ Say M if you want these self tests to build as a module.
+ Say N if you are unsure.
+
config DEBUG_KOBJECT_RELEASE
bool "kobject release debugging"
depends on DEBUG_OBJECTS_TIMERS
--
2.17.1
The cpuidle latency selftest provides support to systematically extract,
analyse and present IPI and timer based wakeup latencies for each CPU
and each idle state available on the system.
The selftest leverages test-cpuidle_latency module's debugfs interface
to interact and extract latency information from the kernel.
The selftest inserts the module if already not inserted, disables all
the idle states and enables them one by one testing the following:
1. Keeping source CPU constant, iterate through all the CPUS measuring
IPI latency for baseline (CPU is busy with cat /dev/random > /dev/null
workload) and then when the CPU is allowed to be at rest
2. Iterating through all the CPUs, sending expected timer durations to
be equivalent to the residency of the deepest idle state enabled
and extracting the difference in time between the time of wakeup and
the expected timer duration
The timer based test produces run to run variance on some intel based
systems that sport a mechansim "C-state pre-wake" which can
pre-wake a CPU from an idle state when timers are armed. For systems and
architectures that don't have this mechansim can leverage timer tests
with the -i option.
To run this test specifically:
$ sudo make -C tools/testing/selftests TARGETS="cpuidle" run_tests
There are a few optional arguments too that the script can take
[-h <help>]
[-i <run timer tests>]
[-m <location of the module>]
[-o <location of the output>]
[-v <verbose> (run on all cpus)]
Default Output location in: tools/testing/selftest/cpuidle/cpuidle.log
To run the test without re-compiling:
$ cd tools/testing/selftest/cpuidle/
$ sudo ./cpuidle.sh
CC: Shuah Khan <[email protected]>
CC: Rafael J. Wysocki <[email protected]>
CC: Daniel Lezcano <[email protected]>
Signed-off-by: Pratik R. Sampat <[email protected]>
---
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/cpuidle/Makefile | 6 +
tools/testing/selftests/cpuidle/cpuidle.sh | 414 +++++++++++++++++++++
tools/testing/selftests/cpuidle/settings | 2 +
4 files changed, 423 insertions(+)
create mode 100644 tools/testing/selftests/cpuidle/Makefile
create mode 100755 tools/testing/selftests/cpuidle/cpuidle.sh
create mode 100644 tools/testing/selftests/cpuidle/settings
diff --git a/tools/testing/selftests/Makefile b/tools/testing/selftests/Makefile
index 6c575cf34a71..561eb67a4839 100644
--- a/tools/testing/selftests/Makefile
+++ b/tools/testing/selftests/Makefile
@@ -7,6 +7,7 @@ TARGETS += cgroup
TARGETS += clone3
TARGETS += core
TARGETS += cpufreq
+TARGETS += cpuidle
TARGETS += cpu-hotplug
TARGETS += drivers/dma-buf
TARGETS += efivarfs
diff --git a/tools/testing/selftests/cpuidle/Makefile b/tools/testing/selftests/cpuidle/Makefile
new file mode 100644
index 000000000000..72fd5d2e974d
--- /dev/null
+++ b/tools/testing/selftests/cpuidle/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+all:
+
+TEST_PROGS := cpuidle.sh
+
+include ../lib.mk
diff --git a/tools/testing/selftests/cpuidle/cpuidle.sh b/tools/testing/selftests/cpuidle/cpuidle.sh
new file mode 100755
index 000000000000..4d5c02ab1eb5
--- /dev/null
+++ b/tools/testing/selftests/cpuidle/cpuidle.sh
@@ -0,0 +1,414 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# CPU-Idle latency selftest provides support to systematically extract,
+# analyse and present IPI and timer based wakeup latencies for each CPU
+# and each idle state available on the system by leveraging the
+# test-cpuidle_latency module
+#
+# Author: Pratik R. Sampat <[email protected]>
+
+LOG=cpuidle.log
+MODULE=/lib/modules/$(uname -r)/kernel/drivers/cpuidle/test-cpuidle_latency.ko
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+
+RUN_TIMER_TEST=0
+VERBOSE=0
+
+DISABLE=1
+ENABLE=0
+
+helpme()
+{
+ printf "Usage: $0 [-h] [-todg args]
+ [-h <help>]
+ [-i <run timer tests>]
+ [-m <location of the module>]
+ [-o <location of the output>]
+ [-v <verbose>]
+ \n"
+ exit 2
+}
+
+parse_arguments()
+{
+ while getopts ht:m:o:vt:it: arg
+ do
+ case $arg in
+ h) # --help
+ helpme
+ ;;
+ i) # run timer tests
+ RUN_TIMER_TEST=1
+ ;;
+ m) # --mod-file
+ MODULE=$OPTARG
+ ;;
+ o) # output log files
+ LOG=$OPTARG
+ ;;
+ v) # Verbose mode
+ VERBOSE=1
+ ;;
+ \?)
+ helpme
+ ;;
+ esac
+ done
+}
+
+ins_mod()
+{
+ debugfs_file=/sys/kernel/debug/latency_test/ipi_latency_ns
+ # Check if the module is already loaded
+ if [ -f "$debugfs_file" ]; then
+ printf "Module already loaded\n\n"
+ return 0
+ fi
+ # Try to load the module
+ if [ ! -f "$MODULE" ]; then
+ printf "$MODULE module does not exist. Exitting\n"
+ exit $ksft_skip
+ fi
+ printf "Inserting $MODULE module\n\n"
+ insmod $MODULE
+ if [ $? != 0 ]; then
+ printf "Insmod $MODULE failed\n"
+ exit $ksft_skip
+ fi
+}
+
+compute_average()
+{
+ arr=("$@")
+ sum=0
+ size=${#arr[@]}
+ if [ $size == 0 ]; then
+ avg=0
+ return 1
+ fi
+ for i in "${arr[@]}"
+ do
+ sum=$((sum + i))
+ done
+ avg=$((sum/size))
+}
+
+cpu_is_online()
+{
+ cpu=$1
+ if [ ! -f "/sys/devices/system/cpu/cpu$cpu/online" ]; then
+ echo 1
+ return
+ fi
+ status=$(cat /sys/devices/system/cpu/cpu$cpu/online)
+ echo $status
+}
+
+# Perform operation on each CPU for the given state
+# $1 - Operation: enable (0) / disable (1)
+# $2 - State to enable
+op_state()
+{
+ for ((cpu=0; cpu<NUM_CPUS; cpu++))
+ do
+ local cpu_status=$(cpu_is_online $cpu)
+ if [ $cpu_status == 0 ]; then
+ continue
+ fi
+ echo $1 > /sys/devices/system/cpu/cpu$cpu/cpuidle/state$2/disable
+ done
+}
+
+cpuidle_enable_state()
+{
+ state=$1
+ op_state $ENABLE $state
+}
+
+cpuidle_disable_state()
+{
+ state=$1
+ op_state $DISABLE $state
+}
+
+# Enable/Disable all stop states for all CPUs
+# $1 - Operation: enable (0) / disable (1)
+op_cpuidle()
+{
+ for ((state=0; state<NUM_STATES; state++))
+ do
+ op_state $1 $state
+ done
+}
+
+# Extract latency in microseconds and convert to nanoseconds
+extract_latency()
+{
+ for ((state=0; state<NUM_STATES; state++))
+ do
+ latency=$(($(cat /sys/devices/system/cpu/cpu0/cpuidle/state$state/latency) * 1000))
+ latency_arr+=($latency)
+ done
+}
+
+# Simple linear search in an array
+# $1 - Element to search for
+# $2 - Array
+element_in()
+{
+ local item="$1"
+ shift
+ for element in "$@";
+ do
+ if [ "$element" == "$item" ]; then
+ return 0
+ fi
+ done
+ return 1
+}
+
+# Parse and return a cpuset with ","(individual) and "-" (range) of CPUs
+# $1 - cpuset string
+parse_cpuset()
+{
+ echo $1 | awk '/-/{for (i=$1; i<=$2; i++)printf "%s%s",i,ORS;next} 1' RS=, FS=-
+}
+
+extract_core_information()
+{
+ declare -a thread_arr
+ for ((cpu=0; cpu<NUM_CPUS; cpu++))
+ do
+ local cpu_status=$(cpu_is_online $cpu)
+ if [ $cpu_status == 0 ]; then
+ continue
+ fi
+
+ siblings=$(cat /sys/devices/system/cpu/cpu$cpu/topology/thread_siblings_list)
+ sib_arr=()
+ for c in $(parse_cpuset $siblings)
+ do
+ sib_arr+=($c)
+ done
+
+ if [ $VERBOSE == 1 ]; then
+ core_arr+=($cpu)
+ for thread in "${sib_arr[@]}"
+ do
+ if [ $cpu == 0 ]; then
+ first_core_arr+=($thread)
+ fi
+ done
+ continue
+ fi
+
+ element_in "${sib_arr[0]}" "${thread_arr[@]}"
+ if [ $? == 0 ]; then
+ continue
+ fi
+ core_arr+=(${sib_arr[0]})
+
+ for thread in "${sib_arr[@]}"
+ do
+ thread_arr+=($thread)
+ if [ $cpu == 0 ]; then
+ first_core_arr+=($thread)
+ fi
+ done
+ done
+}
+
+# Run the IPI test
+# $1 run for baseline - busy cpu or regular environment
+# $2 destination cpu
+ipi_test_once()
+{
+ dest_cpu=$2
+ if [ "$1" = "baseline" ]; then
+ # Keep the CPU busy
+ taskset -c $dest_cpu cat /dev/random > /dev/null &
+ task_pid=$!
+ # Wait for the workload to achieve 100% CPU usage
+ sleep 1
+ fi
+ taskset 0x1 echo $dest_cpu > /sys/kernel/debug/latency_test/ipi_cpu_dest
+ ipi_latency=$(cat /sys/kernel/debug/latency_test/ipi_latency_ns)
+ src_cpu=$(cat /sys/kernel/debug/latency_test/ipi_cpu_src)
+ if [ "$1" = "baseline" ]; then
+ kill $task_pid
+ wait $task_pid 2>/dev/null
+ fi
+}
+
+# Incrementally Enable idle states one by one and compute the latency
+run_ipi_tests()
+{
+ extract_latency
+ # Disable idle states for CPUs
+ op_cpuidle $DISABLE
+
+ declare -a avg_arr
+ echo -e "--IPI Latency Test---" | tee -a $LOG
+
+ echo -e "--Baseline IPI Latency measurement: CPU Busy--" >> $LOG
+ printf "%s %10s %12s\n" "SRC_CPU" "DEST_CPU" "IPI_Latency(ns)" >> $LOG
+ for cpu in "${core_arr[@]}"
+ do
+ local cpu_status=$(cpu_is_online $cpu)
+ if [ $cpu_status == 0 ]; then
+ continue
+ fi
+ ipi_test_once "baseline" $cpu
+ printf "%-3s %10s %12s\n" $src_cpu $cpu $ipi_latency >> $LOG
+ # Skip computing latency average from the source CPU to avoid bias
+ element_in "$cpu" "${first_core_arr[@]}"
+ if [ $? == 0 ]; then
+ continue
+ fi
+ avg_arr+=($ipi_latency)
+ done
+ compute_average "${avg_arr[@]}"
+ echo -e "Baseline Avg IPI latency(ns): $avg" | tee -a $LOG
+
+ for ((state=0; state<NUM_STATES; state++))
+ do
+ unset avg_arr
+ echo -e "---Enabling state: $state---" >> $LOG
+ cpuidle_enable_state $state
+ printf "%s %10s %12s\n" "SRC_CPU" "DEST_CPU" "IPI_Latency(ns)" >> $LOG
+ for cpu in "${core_arr[@]}"
+ do
+ local cpu_status=$(cpu_is_online $cpu)
+ if [ $cpu_status == 0 ]; then
+ continue
+ fi
+ # Running IPI test and logging results
+ sleep 1
+ ipi_test_once "test" $cpu
+ printf "%-3s %10s %12s\n" $src_cpu $cpu $ipi_latency >> $LOG
+ # Skip computing latency average from the source CPU to avoid bias
+ element_in "$cpu" "${first_core_arr[@]}"
+ if [ $? == 0 ]; then
+ continue
+ fi
+ avg_arr+=($ipi_latency)
+ done
+ compute_average "${avg_arr[@]}"
+ echo -e "Expected IPI latency(ns): ${latency_arr[$state]}" >> $LOG
+ echo -e "Observed Avg IPI latency(ns) - State $state: $avg" | tee -a $LOG
+ cpuidle_disable_state $state
+ done
+}
+
+# Extract the residency in microseconds and convert to nanoseconds.
+# Add 200 ns so that the timer stays for a little longer than the residency
+extract_residency()
+{
+ for ((state=0; state<NUM_STATES; state++))
+ do
+ residency=$(($(cat /sys/devices/system/cpu/cpu0/cpuidle/state$state/residency) * 1000 + 200))
+ residency_arr+=($residency)
+ done
+}
+
+# Run the Timeout test
+# $1 run for baseline - busy cpu or regular environment
+# $2 destination cpu
+# $3 timeout
+timeout_test_once()
+{
+ dest_cpu=$2
+ if [ "$1" = "baseline" ]; then
+ # Keep the CPU busy
+ taskset -c $dest_cpu cat /dev/random > /dev/null &
+ task_pid=$!
+ # Wait for the workload to achieve 100% CPU usage
+ sleep 1
+ fi
+ taskset -c $dest_cpu echo $3 > /sys/kernel/debug/latency_test/timeout_expected_ns
+ # Wait for the result to populate
+ sleep 0.1
+ timeout_diff=$(cat /sys/kernel/debug/latency_test/timeout_diff_ns)
+ src_cpu=$(cat /sys/kernel/debug/latency_test/timeout_cpu_src)
+ if [ "$1" = "baseline" ]; then
+ kill $task_pid
+ wait $task_pid 2>/dev/null
+ fi
+}
+
+run_timeout_tests()
+{
+ extract_residency
+ # Disable idle states for all CPUs
+ op_cpuidle $DISABLE
+
+ declare -a avg_arr
+ echo -e "\n--Timeout Latency Test--" | tee -a $LOG
+
+ echo -e "--Baseline Timeout Latency measurement: CPU Busy--" >> $LOG
+ printf "%s %10s %10s\n" "Wakeup_src" "Baseline_delay(ns)">> $LOG
+ for cpu in "${core_arr[@]}"
+ do
+ local cpu_status=$(cpu_is_online $cpu)
+ if [ $cpu_status == 0 ]; then
+ continue
+ fi
+ timeout_test_once "baseline" $cpu 1000000
+ printf "%-3s %13s\n" $src_cpu $timeout_diff >> $LOG
+ avg_arr+=($timeout_diff)
+ done
+ compute_average "${avg_arr[@]}"
+ echo -e "Baseline Avg timeout diff(ns): $avg" | tee -a $LOG
+
+ for ((state=0; state<NUM_STATES; state++))
+ do
+ unset avg_arr
+ echo -e "---Enabling state: $state---" >> $LOG
+ cpuidle_enable_state $state
+ printf "%s %10s %10s\n" "Wakeup_src" "Baseline_delay(ns)" "Delay(ns)" >> $LOG
+ for cpu in "${core_arr[@]}"
+ do
+ local cpu_status=$(cpu_is_online $cpu)
+ if [ $cpu_status == 0 ]; then
+ continue
+ fi
+ timeout_test_once "test" $cpu 1000000
+ printf "%-3s %13s %18s\n" $src_cpu $baseline_timeout_diff $timeout_diff >> $LOG
+ avg_arr+=($timeout_diff)
+ done
+ compute_average "${avg_arr[@]}"
+ echo -e "Expected timeout(ns): ${residency_arr[$state]}" >> $LOG
+ echo -e "Observed Avg timeout diff(ns) - State $state: $avg" | tee -a $LOG
+ cpuidle_disable_state $state
+ done
+}
+
+declare -a residency_arr
+declare -a latency_arr
+declare -a core_arr
+declare -a first_core_arr
+
+parse_arguments $@
+
+rm -f $LOG
+touch $LOG
+NUM_CPUS=$(nproc --all)
+NUM_STATES=$(ls -1 /sys/devices/system/cpu/cpu0/cpuidle/ | wc -l)
+
+extract_core_information
+
+ins_mod $MODULE
+
+run_ipi_tests
+if [ $RUN_TIMER_TEST == 1 ]; then
+ run_timeout_tests
+fi
+
+# Enable all idle states for all CPUs
+op_cpuidle $ENABLE
+printf "Removing $MODULE module\n"
+printf "Full Output logged at: $LOG\n"
+rmmod $MODULE
diff --git a/tools/testing/selftests/cpuidle/settings b/tools/testing/selftests/cpuidle/settings
new file mode 100644
index 000000000000..a26c38a70d77
--- /dev/null
+++ b/tools/testing/selftests/cpuidle/settings
@@ -0,0 +1,2 @@
+timeout=0
+
--
2.17.1
Hi @Rafael and @Shuah,
Gentle ping.
Is there any feedback on this patch-set?
Quick summary and history:
1. The patchset introduces a kernel module and a bash selftest driver to
estimate wakeup latency caused by entering idle states
2. The patchset has seemed to provide useful feedback on latency of idle
states
on the IBM POWER architecture
3. It also seems to also be providing desirable results on Intel
machines with
the IPI mechanism (Timer tests are optional here due to some Intel
processors having a pre-wakeup feature and may not tend to actual idle
latency) as reviewed by Doug Smythies.
Intel numbers for reference: https://lkml.org/lkml/2021/4/13/785
--
Thanks
Pratik
On 30/04/21 1:58 pm, Pratik R. Sampat wrote:
> Changelog RFC v4 --> PATCH v5:
> 1. Added a CPU online check prior to parsing the CPU topology to avoid
> parsing topologies for CPUs unavailable for the latency test
> 2. Added comment describing the selftest in cpuidle.sh
>
> As I have made changes to cpuidle.sh's working, hence dropping
> "Reviewed-by" from Doug Smythies for the second patch, while retaining
> it for the first patch.
>
> RFC v4: https://lkml.org/lkml/2021/4/12/99
> ---
> A kernel module + userspace driver to estimate the wakeup latency
> caused by going into stop states. The motivation behind this program is
> to find significant deviations behind advertised latency and residency
> values.
>
> The patchset measures latencies for two kinds of events. IPIs and Timers
> As this is a software-only mechanism, there will additional latencies of
> the kernel-firmware-hardware interactions. To account for that, the
> program also measures a baseline latency on a 100 percent loaded CPU
> and the latencies achieved must be in view relative to that.
>
> To achieve this, we introduce a kernel module and expose its control
> knobs through the debugfs interface that the selftests can engage with.
>
> The kernel module provides the following interfaces within
> /sys/kernel/debug/latency_test/ for,
>
> IPI test:
> ipi_cpu_dest = Destination CPU for the IPI
> ipi_cpu_src = Origin of the IPI
> ipi_latency_ns = Measured latency time in ns
> Timeout test:
> timeout_cpu_src = CPU on which the timer to be queued
> timeout_expected_ns = Timer duration
> timeout_diff_ns = Difference of actual duration vs expected timer
>
> Sample output on a POWER9 system is as follows:
> # --IPI Latency Test---
> # Baseline Average IPI latency(ns): 3114
> # Observed Average IPI latency(ns) - State0: 3265
> # Observed Average IPI latency(ns) - State1: 3507
> # Observed Average IPI latency(ns) - State2: 3739
> # Observed Average IPI latency(ns) - State3: 3807
> # Observed Average IPI latency(ns) - State4: 17070
> # Observed Average IPI latency(ns) - State5: 1038174
> # Observed Average IPI latency(ns) - State6: 1068784
> #
> # --Timeout Latency Test--
> # Baseline Average timeout diff(ns): 1420
> # Observed Average timeout diff(ns) - State0: 1640
> # Observed Average timeout diff(ns) - State1: 1764
> # Observed Average timeout diff(ns) - State2: 1715
> # Observed Average timeout diff(ns) - State3: 1845
> # Observed Average timeout diff(ns) - State4: 16581
> # Observed Average timeout diff(ns) - State5: 939977
> # Observed Average timeout diff(ns) - State6: 1073024
>
>
> Things to keep in mind:
>
> 1. This kernel module + bash driver does not guarantee idleness on a
> core when the IPI and the Timer is armed. It only invokes sleep and
> hopes that the core is idle once the IPI/Timer is invoked onto it.
> Hence this program must be run on a completely idle system for best
> results
>
> 2. Even on a completely idle system, there maybe book-keeping tasks or
> jitter tasks that can run on the core we want idle. This can create
> outliers in the latency measurement. Thankfully, these outliers
> should be large enough to easily weed them out.
>
> 3. A userspace only selftest variant was also sent out as RFC based on
> suggestions over the previous patchset to simply the kernel
> complexeity. However, a userspace only approach had more noise in
> the latency measurement due to userspace-kernel interactions
> which led to run to run variance and a lesser accurate test.
> Another downside of the nature of a userspace program is that it
> takes orders of magnitude longer to complete a full system test
> compared to the kernel framework.
> RFC patch: https://lkml.org/lkml/2020/9/2/356
>
> 4. For Intel Systems, the Timer based latencies don't exactly give out
> the measure of idle latencies. This is because of a hardware
> optimization mechanism that pre-arms a CPU when a timer is set to
> wakeup. That doesn't make this metric useless for Intel systems,
> it just means that is measuring IPI/Timer responding latency rather
> than idle wakeup latencies.
> (Source: https://lkml.org/lkml/2020/9/2/610)
> For solution to this problem, a hardware based latency analyzer is
> devised by Artem Bityutskiy from Intel.
> https://youtu.be/Opk92aQyvt0?t=8266
> https://intel.github.io/wult/
>
> Pratik R. Sampat (2):
> cpuidle: Extract IPI based and timer based wakeup latency from idle
> states
> selftest/cpuidle: Add support for cpuidle latency measurement
>
> drivers/cpuidle/Makefile | 1 +
> drivers/cpuidle/test-cpuidle_latency.c | 157 ++++++++
> lib/Kconfig.debug | 10 +
> tools/testing/selftests/Makefile | 1 +
> tools/testing/selftests/cpuidle/Makefile | 6 +
> tools/testing/selftests/cpuidle/cpuidle.sh | 414 +++++++++++++++++++++
> tools/testing/selftests/cpuidle/settings | 2 +
> 7 files changed, 591 insertions(+)
> create mode 100644 drivers/cpuidle/test-cpuidle_latency.c
> create mode 100644 tools/testing/selftests/cpuidle/Makefile
> create mode 100755 tools/testing/selftests/cpuidle/cpuidle.sh
> create mode 100644 tools/testing/selftests/cpuidle/settings
>