Changelog v3-->v4
Based on review comments by Doug Smythies,
1. Parsing the thread_siblings_list for CPU topology information to
correctly identify the cores the test should run on in
default(quick) mode.
2. The source CPU to source CPU interaction in the IPI test will always
result in a lower latency and cause a bias in the average, hence
avoid adding the latency to be averaged for same cpu IPIs. The
latency will still be displayed in the detailed logs.
RFC v3: https://lkml.org/lkml/2021/4/4/31
---
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 Rajesh 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 | 402 +++++++++++++++++++++
tools/testing/selftests/cpuidle/settings | 2 +
7 files changed, 579 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
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
Signed-off-by: Pratik Rajesh Sampat <[email protected]>
---
tools/testing/selftests/Makefile | 1 +
tools/testing/selftests/cpuidle/Makefile | 6 +
tools/testing/selftests/cpuidle/cpuidle.sh | 402 +++++++++++++++++++++
tools/testing/selftests/cpuidle/settings | 2 +
4 files changed, 411 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..2d9afa5242cd
--- /dev/null
+++ b/tools/testing/selftests/cpuidle/cpuidle.sh
@@ -0,0 +1,402 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+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<=$2; i++)printf "%s%s",i,ORS;next} 1' RS=, FS=-
+}
+
+extract_core_information()
+{
+ declare -a thread_arr
+ for ((cpu=0; cpu<NUM_CPUS; cpu++))
+ do
+ sib_arr=()
+ siblings=$(cat /sys/devices/system/cpu/cpu$cpu/topology/thread_siblings_list)
+ 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 $MODULE
diff --git a/tools/testing/selftests/cpuidle/settings b/tools/testing/selftests/cpuidle/settings
new file mode 100644
index 000000000000..a26c38a70d77
--- /dev/null
+++ b/tools/testing/selftests/cpuidle/settings
@@ -0,0 +1,2 @@
+timeout=0
+
--
2.17.1
Introduce a mechanism to fire directed IPIs from a specified source CPU
to a specified target CPU and measure the difference in time incurred on
wakeup.
Also, introduce a mechanism to queue a HR timer on a specified CPU and
subsequently measure the time taken to wakeup the CPU.
Finally define a simple debugfs interface to control the knobs to fire
the IPI and Timer events on specified CPU and view their incurred idle
wakeup latencies.
Signed-off-by: Pratik Rajesh Sampat <[email protected]>
---
drivers/cpuidle/Makefile | 1 +
drivers/cpuidle/test-cpuidle_latency.c | 157 +++++++++++++++++++++++++
lib/Kconfig.debug | 10 ++
3 files changed, 168 insertions(+)
create mode 100644 drivers/cpuidle/test-cpuidle_latency.c
diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index 26bbc5e74123..3b4ee06a9164 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile
@@ -8,6 +8,7 @@ obj-$(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 2779c29d9981..60fa46a99a4f 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
Hi Pratik,
V4 seems fine. Thank you.
On Mon, Apr 12, 2021 at 12:43 AM Pratik Rajesh Sampat
<[email protected]> wrote:
>
> Changelog v3-->v4
> Based on review comments by Doug Smythies,
> 1. Parsing the thread_siblings_list for CPU topology information to
> correctly identify the cores the test should run on in
> default(quick) mode.
> 2. The source CPU to source CPU interaction in the IPI test will always
> result in a lower latency and cause a bias in the average, hence
> avoid adding the latency to be averaged for same cpu IPIs. The
> latency will still be displayed in the detailed logs.
>
> RFC v3: https://lkml.org/lkml/2021/4/4/31
Example output for an Intel i5-10600K, HWP active, performance mode.
System very idle:
$ sudo ./cpuidle.sh -v -i
Inserting /lib/modules/5.12.0-rc7-prs-v4/kernel/drivers/cpuidle/test-cpuidle_latency.ko
module
--IPI Latency Test---
Baseline Avg IPI latency(ns): 686
Observed Avg IPI latency(ns) - State 0: 468
Observed Avg IPI latency(ns) - State 1: 956
Observed Avg IPI latency(ns) - State 2: 17936
Observed Avg IPI latency(ns) - State 3: 17968
--Timeout Latency Test--
Baseline Avg timeout diff(ns): 445
Observed Avg timeout diff(ns) - State 0: 377
Observed Avg timeout diff(ns) - State 1: 630
Observed Avg timeout diff(ns) - State 2: 322812
Observed Avg timeout diff(ns) - State 3: 306067
Removing /lib/modules/5.12.0-rc7-prs-v4/kernel/drivers/cpuidle/test-cpuidle_latency.ko
module
Full Output logged at: cpuidle.log
$ grep . /sys/devices/system/cpu/cpu7/cpuidle/state*/residency
/sys/devices/system/cpu/cpu7/cpuidle/state0/residency:0
/sys/devices/system/cpu/cpu7/cpuidle/state1/residency:1
/sys/devices/system/cpu/cpu7/cpuidle/state2/residency:360
/sys/devices/system/cpu/cpu7/cpuidle/state3/residency:3102
$ grep . /sys/devices/system/cpu/cpu7/cpuidle/state*/latency
/sys/devices/system/cpu/cpu7/cpuidle/state0/latency:0
/sys/devices/system/cpu/cpu7/cpuidle/state1/latency:1
/sys/devices/system/cpu/cpu7/cpuidle/state2/latency:120
/sys/devices/system/cpu/cpu7/cpuidle/state3/latency:1034
... Doug
Hi Pratik,
On Mon, Apr 12, 2021 at 12:43 AM Pratik Rajesh Sampat
<[email protected]> wrote:
>
> 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.
>
> Signed-off-by: Pratik Rajesh Sampat <[email protected]>
Reviewed-by: Doug Smythies <[email protected]>
Hi Pratik,
On Mon, Apr 12, 2021 at 12:43 AM Pratik Rajesh Sampat
<[email protected]> wrote:
>
> 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
>
> Signed-off-by: Pratik Rajesh Sampat <[email protected]>
Reviewed-by: Doug Smythies <[email protected]>
...