Fire directed smp_call_function_single IPIs from a specified source CPU to the specified target CPU to reduce the noise we have to wade through in the trace log. The module is based on the idea written by Srivatsa Bhat and maintained by Vaidyanathan Srinivasan internally.

Queue HR timer and measure jitter. Wakeup latency measurement for idle states using hrtimer. Echo a value in ns to timer_test_function and watch trace. A HRtimer will be queued and when it fires the expected wakeup vs actual wakeup is computes and delay printed in ns.

Implemented as a module which utilizes debugfs so that it can be integrated with selftests.

To include the module, check option and include as module kernel hacking -> Cpuidle latency selftests

[srivatsa.bhat@linux.vnet.ibm.com: Initial implementation in cpidle/sysfs]

[svaidy@linux.vnet.ibm.com: wakeup latency measurements using hrtimer and fix some of the time calculation]

[ego@linux.vnet.ibm.com: Fix some whitespace and tab errors and increase the resolution of IPI wakeup]

Signed-off-by: Pratik Rajesh Sampat psampat@linux.ibm.com --- drivers/cpuidle/Makefile | 1 + drivers/cpuidle/test-cpuidle_latency.c | 150 +++++++++++++++++++++++++ lib/Kconfig.debug | 10 ++ 3 files changed, 161 insertions(+) create mode 100644 drivers/cpuidle/test-cpuidle_latency.c

diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile index f07800cbb43f..2ae05968078c 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..61574665e972 --- /dev/null +++ b/drivers/cpuidle/test-cpuidle_latency.c @@ -0,0 +1,150 @@ +// 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 */ +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 */ +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.time_start = ktime_get(); + timer_wakeup.src_cpu = smp_processor_id(); + timer_wakeup.timeout = ns; + + 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 *value) +{ + *value = 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 *value) +{ + *value = 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 d74ac0fd6b2d..e2283790245a 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1375,6 +1375,16 @@ 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

This patch adds support to trace IPI based and timer based wakeup latency from idle states

Latches onto the test-cpuidle_latency kernel module using the debugfs interface to send IPIs or schedule a timer based event, which in-turn populates the debugfs with the latency measurements.

Currently for the IPI and timer tests; first disable all idle states and then test for latency measurements incrementally enabling each state

Signed-off-by: Pratik Rajesh Sampat psampat@linux.ibm.com --- tools/testing/selftests/Makefile | 1 + tools/testing/selftests/cpuidle/Makefile | 6 + tools/testing/selftests/cpuidle/cpuidle.sh | 257 +++++++++++++++++++++ tools/testing/selftests/cpuidle/settings | 1 + 4 files changed, 265 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 1195bd85af38..ab6cf51f3518 100644 --- a/tools/testing/selftests/Makefile +++ b/tools/testing/selftests/Makefile @@ -7,6 +7,7 @@ TARGETS += capabilities TARGETS += cgroup TARGETS += clone3 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..5c313a3abb0c --- /dev/null +++ b/tools/testing/selftests/cpuidle/cpuidle.sh @@ -0,0 +1,257 @@ +#!/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 + +helpme() +{ + printf "Usage: $0 [-h] [-todg args] + [-h <help>] + [-m <location of the module>] + [-o <location of the output>] + \n" + exit 2 +} + +parse_arguments() +{ + while getopts ht:m:o: arg + do + case $arg in + h) # --help + helpme + ;; + m) # --mod-file + MODULE=$OPTARG + ;; + o) # output log files + LOG=$OPTARG + ;; + ?) + helpme + ;; + esac + done +} + +ins_mod() +{ + if [ ! -f "$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=${#arr[@]} + for i in "${arr[@]}" + do + sum=$((sum + i)) + done + avg=$((sum/size)) +} + +# Disable all stop states +disable_idle() +{ + for ((cpu=0; cpu<NUM_CPUS; cpu++)) + do + for ((state=0; state<NUM_STATES; state++)) + do + echo 1 > /sys/devices/system/cpu/cpu$cpu/cpuidle/state$state/disable + done + done +} + +# 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 + echo $1 > /sys/devices/system/cpu/cpu$cpu/cpuidle/state$2/disable + done +} + +# Extract latency in microseconds and convert to nanoseconds +extract_latency() +{ + for ((state=0; state<NUM_STATES; state++)) + do + latency=$(($(cat /sys/devices/system/cpu/cpu0/cpuidle/state$state/latency) * 1000)) + latency_arr+=($latency) + done +} + +# 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 + declare -a avg_arr + echo -e "--IPI Latency Test---" >> $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=0; cpu<NUM_CPUS; cpu++)) + do + ipi_test_once "baseline" $cpu + printf "%-3s %10s %12s\n" $src_cpu $cpu $ipi_latency >> $LOG + avg_arr+=($ipi_latency) + done + compute_average "${avg_arr[@]}" + echo -e "Baseline Average IPI latency(ns): $avg" >> $LOG + + for ((state=0; state<NUM_STATES; state++)) + do + unset avg_arr + echo -e "---Enabling state: $state---" >> $LOG + op_state 0 $state + printf "%s %10s %12s\n" "SRC_CPU" "DEST_CPU" "IPI_Latency(ns)" >> $LOG + for ((cpu=0; cpu<NUM_CPUS; cpu++)) + do + # Running IPI test and logging results + sleep 1 + ipi_test_once "test" $cpu + printf "%-3s %10s %12s\n" $src_cpu $cpu $ipi_latency >> $LOG + avg_arr+=($ipi_latency) + done + compute_average "${avg_arr[@]}" + echo -e "Expected IPI latency(ns): ${latency_arr[$state]}" >> $LOG + echo -e "Observed Average IPI latency(ns): $avg" >> $LOG + op_state 1 $state + done +} + +# Extract the residency in microseconds and convert to nanoseconds. +# Add 100 ns so that the timer stays for a little longer than the residency +extract_residency() +{ + for ((state=0; state<NUM_STATES; state++)) + do + residency=$(($(cat /sys/devices/system/cpu/cpu0/cpuidle/state$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 + declare -a avg_arr + echo -e "\n--Timeout Latency Test--" >> $LOG + + echo -e "--Baseline Timeout Latency measurement: CPU Busy--" >> $LOG + printf "%s %10s %10s\n" "Wakeup_src" "Baseline_delay(ns)">> $LOG + for ((cpu=0; cpu<NUM_CPUS; cpu++)) + do + timeout_test_once "baseline" $cpu ${residency_arr[0]} + printf "%-3s %13s\n" $src_cpu $timeout_diff >> $LOG + avg_arr+=($timeout_diff) + done + compute_average "${avg_arr[@]}" + echo -e "Baseline Average timeout diff(ns): $avg" >> $LOG + + for ((state=0; state<NUM_STATES; state++)) + do + echo -e "---Enabling state: $state---" >> $LOG + op_state 0 $state + printf "%s %10s %10s\n" "Wakeup_src" "Baseline_delay(ns)" "Delay(ns)" >> $LOG + unset avg_arr + for ((cpu=0; cpu<NUM_CPUS; cpu++)) + do + timeout_test_once "test" $cpu ${residency_arr[$state]} + 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 Average timeout diff(ns): $avg" >> $LOG + op_state 1 $state + done +} + +declare -a residency_arr +declare -a latency_arr + +# Parse arguments +parse_arguments $@ + +rm -f $LOG +touch $LOG +NUM_CPUS=$(nproc --all) +NUM_STATES=$(ls -1 /sys/devices/system/cpu/cpu0/cpuidle/ | wc -l) + +# Insert the module +ins_mod $MODULE + +printf "Started IPI latency tests\n" +run_ipi_tests + +printf "Started Timer latency tests\n" +run_timeout_tests + +printf "Removing $MODULE module\n" +printf "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..e7b9417537fb --- /dev/null +++ b/tools/testing/selftests/cpuidle/settings @@ -0,0 +1 @@ +timeout=0