[RFC v2 0/2] CPU-Idle latency selftest framework

[RFC v2 0/2] CPU-Idle latency selftest framework

[Aboorva Devarajan]

Changelog: v1 -> v2

* Rebased on v6.5-rc6
* Moved the test directory to powerpc debugfs
* Minimal code refactoring

RFC v1: 
https://lore.kernel.org/all/20210611124154.56427-1-psampat@linux.ibm.com/

Other related RFC:
https://lore.kernel.org/all/20210430082804.38018-1-psampat@linux.ibm.com/

Userspace selftest:
https://lkml.org/lkml/2020/9/2/356

----

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 be 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/powerpc/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 is as follows:

# --IPI Latency Test---
# Baseline Avg IPI latency(ns): 2720
# Observed Avg IPI latency(ns) - State snooze: 2565
# Observed Avg IPI latency(ns) - State stop0_lite: 3856
# Observed Avg IPI latency(ns) - State stop0: 3670
# Observed Avg IPI latency(ns) - State stop1: 3872
# Observed Avg IPI latency(ns) - State stop2: 17421
# Observed Avg IPI latency(ns) - State stop4: 1003922
# Observed Avg IPI latency(ns) - State stop5: 1058870
#
# --Timeout Latency Test--
# Baseline Avg timeout diff(ns): 1435
# Observed Avg timeout diff(ns) - State snooze: 1709
# Observed Avg timeout diff(ns) - State stop0_lite: 2028
# Observed Avg timeout diff(ns) - State stop0: 1954
# Observed Avg timeout diff(ns) - State stop1: 1895
# Observed Avg timeout diff(ns) - State stop2: 14556
# Observed Avg timeout diff(ns) - State stop4: 873988
# Observed Avg timeout diff(ns) - State stop5: 959137

Aboorva Devarajan (2):
  powerpc/cpuidle: cpuidle wakeup latency based on IPI and timer events
  powerpc/selftest: Add support for cpuidle latency measurement

 arch/powerpc/Kconfig.debug                    |  10 +
 arch/powerpc/kernel/Makefile                  |   1 +
 arch/powerpc/kernel/test_cpuidle_latency.c    | 156 ++++++
 tools/testing/selftests/powerpc/Makefile      |   1 +
 .../powerpc/cpuidle_latency/.gitignore        |   2 +
 .../powerpc/cpuidle_latency/Makefile          |   6 +
 .../cpuidle_latency/cpuidle_latency.sh        | 443 ++++++++++++++++++
 .../powerpc/cpuidle_latency/settings          |   1 +
 8 files changed, 620 insertions(+)
 create mode 100644 arch/powerpc/kernel/test_cpuidle_latency.c
 create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/.gitignore
 create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/Makefile
 create mode 100755 tools/testing/selftests/powerpc/cpuidle_latency/cpuidle_latency.sh
 create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/settings

-- 
2.25.1

[RFC v2 1/2] powerpc/cpuidle: cpuidle wakeup latency based on IPI and timer events

[Aboorva Devarajan]

From: Pratik R. Sampat <psampat@linux.ibm.com>

Introduce a mechanism to fire directed IPIs from a source CPU to a
specified target CPU and measure the time incurred on waking up the
target CPU in response.

Also, introduce a mechanism to queue a hrtimer on a specified CPU and
subsequently measure the time taken to wakeup the CPU.

Define a simple debugfs interface that allows for adjusting the
settings to trigger IPI and timer events on a designated CPU, and to
observe the resulting cpuidle wakeup latencies.

Signed-off-by: Pratik R. Sampat <psampat@linux.ibm.com>
Signed-off-by: Aboorva Devarajan <aboorvad@linux.vnet.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
---
 arch/powerpc/Kconfig.debug                 |  10 ++
 arch/powerpc/kernel/Makefile               |   1 +
 arch/powerpc/kernel/test_cpuidle_latency.c | 156 +++++++++++++++++++++
 3 files changed, 167 insertions(+)
 create mode 100644 arch/powerpc/kernel/test_cpuidle_latency.c

diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 2a54fadbeaf5..e175fc3028ac 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/arch/powerpc/Kconfig.debug
@@ -391,3 +391,13 @@ config KASAN_SHADOW_OFFSET
 	default 0xe0000000 if PPC32
 	default 0xa80e000000000000 if PPC_BOOK3S_64
 	default 0xa8001c0000000000 if PPC_BOOK3E_64
+
+config CPUIDLE_LATENCY_SELFTEST
+	tristate "Cpuidle latency selftests"
+	depends on CPU_IDLE
+	help
+	  Provides a kernel module that run tests using the IPI and
+	  timers to measure cpuidle latency.
+
+	  Say M if you want these self tests to build as a module.
+	  Say N if you are unsure.
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 2919433be355..3205ecbd9d8f 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -87,6 +87,7 @@ obj-$(CONFIG_PPC_WATCHDOG)	+= watchdog.o
 obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
 obj-$(CONFIG_PPC_DAWR)		+= dawr.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_ppc970.o cpu_setup_pa6t.o
+obj-$(CONFIG_CPUIDLE_LATENCY_SELFTEST)  += test_cpuidle_latency.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_power.o
 obj-$(CONFIG_PPC_BOOK3S_64)	+= mce.o mce_power.o
 obj-$(CONFIG_PPC_BOOK3E_64)	+= exceptions-64e.o idle_64e.o
diff --git a/arch/powerpc/kernel/test_cpuidle_latency.c b/arch/powerpc/kernel/test_cpuidle_latency.c
new file mode 100644
index 000000000000..3c3c119389c1
--- /dev/null
+++ b/arch/powerpc/kernel/test_cpuidle_latency.c
@@ -0,0 +1,156 @@
+// 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 hrtimer_callback(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 = hrtimer_callback;
+	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;
+}
+
+/*
+ * Send a directed IPI from the current CPU (source) to the destination CPU and
+ * measure the latency on wakeup.
+ */
+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;
+}
+
+/* Queue a hrtimer on a specified desitination CPU and measure the time taken to
+ * wakeup the CPU.
+ */
+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", arch_debugfs_dir);
+	if (!dir) {
+		pr_alert("latency_test: failed to create /sys/kernel/debug/powerpc/latency_test\n");
+		return -1;
+	}
+	temp = debugfs_create_file("ipi_cpu_dest", 0644, dir, NULL, &ipi_ops);
+	if (!temp) {
+		pr_alert("latency_test: failed to create /sys/kernel/debug/powerpc/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", 0644, dir, NULL, &timeout_ops);
+	if (!temp) {
+		pr_alert("latency_test: failed to create /sys/kernel/debug/powerpc/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");
-- 
2.25.1

[RFC v2 2/2] powerpc/selftest: Add support for cpuidle latency measurement

[Aboorva Devarajan]

From: Pratik R. Sampat <psampat@linux.ibm.com>

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 cores and pick
   a single CPU for each core measuring IPI latency for baseline
   (CPU is busy with cat /dev/random > /dev/null workload) and then
   when the CPU is idle.
2. Iterating through all the CPU cores and selecting one CPU for each
   core, then, the expected timer durations to be equivalent to the
   residency of the deepest idle state enabled is sent to the selected
   target CPU, then the difference between the expected timer duration
   and the time of wakeup is determined.

To run this test specifically:
$ sudo make -C tools/testing/selftests \
  TARGETS="powerpc/cpuidle_latency" 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>]
        [-s <source cpu for ipi test>]
        [-o <location of the output>]
        [-v <verbose> (run on all cpus)]

Default Output location in:
tools/testing/selftests/powerpc/cpuidle_latency/cpuidle_latency.log

To run the test without re-compiling:
$ cd tools/testing/selftest/powerpc/cpuidle_latency/
$ sudo ./cpuidle_latency.sh

Signed-off-by: Pratik R. Sampat <psampat@linux.ibm.com>
Signed-off-by: Aboorva Devarajan <aboorvad@linux.vnet.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
---
 tools/testing/selftests/powerpc/Makefile      |   1 +
 .../powerpc/cpuidle_latency/.gitignore        |   2 +
 .../powerpc/cpuidle_latency/Makefile          |   6 +
 .../cpuidle_latency/cpuidle_latency.sh        | 443 ++++++++++++++++++
 .../powerpc/cpuidle_latency/settings          |   1 +
 5 files changed, 453 insertions(+)
 create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/.gitignore
 create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/Makefile
 create mode 100755 tools/testing/selftests/powerpc/cpuidle_latency/cpuidle_latency.sh
 create mode 100644 tools/testing/selftests/powerpc/cpuidle_latency/settings

diff --git a/tools/testing/selftests/powerpc/Makefile b/tools/testing/selftests/powerpc/Makefile
index 49f2ad1793fd..efac7270ce1f 100644
--- a/tools/testing/selftests/powerpc/Makefile
+++ b/tools/testing/selftests/powerpc/Makefile
@@ -17,6 +17,7 @@ SUB_DIRS = alignment		\
 	   benchmarks		\
 	   cache_shape		\
 	   copyloops		\
+	   cpuidle_latency	\
 	   dexcr		\
 	   dscr			\
 	   mm			\
diff --git a/tools/testing/selftests/powerpc/cpuidle_latency/.gitignore b/tools/testing/selftests/powerpc/cpuidle_latency/.gitignore
new file mode 100644
index 000000000000..987f8852dc59
--- /dev/null
+++ b/tools/testing/selftests/powerpc/cpuidle_latency/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+cpuidle_latency.log
diff --git a/tools/testing/selftests/powerpc/cpuidle_latency/Makefile b/tools/testing/selftests/powerpc/cpuidle_latency/Makefile
new file mode 100644
index 000000000000..04492b6d2582
--- /dev/null
+++ b/tools/testing/selftests/powerpc/cpuidle_latency/Makefile
@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: GPL-2.0
+all:
+
+TEST_PROGS := cpuidle_latency.sh
+
+include ../../lib.mk
diff --git a/tools/testing/selftests/powerpc/cpuidle_latency/cpuidle_latency.sh b/tools/testing/selftests/powerpc/cpuidle_latency/cpuidle_latency.sh
new file mode 100755
index 000000000000..f7b7a9dc2e08
--- /dev/null
+++ b/tools/testing/selftests/powerpc/cpuidle_latency/cpuidle_latency.sh
@@ -0,0 +1,443 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+#
+# CPU-Idle latency selftest enables systematic retrieval and presentation
+# of IPI and timer-triggered wake-up latencies for every CPU and available
+# system idle state by leveraging the test_cpuidle_latency module.
+#
+# Author: Pratik R. Sampat  <psampat at linux.ibm.com>
+# Author: Aboorva Devarajan <aboorvad at linux.ibm.com>
+
+DISABLE=1
+ENABLE=0
+
+LOG=cpuidle_latency.log
+MODULE=/lib/modules/$(uname -r)/kernel/arch/powerpc/kernel/test_cpuidle_latency.ko
+
+# Kselftest framework requirement - SKIP code is 4.
+ksft_skip=4
+exit_status=0
+
+RUN_TIMER_TEST=1
+TIMEOUT=1000000
+VERBOSE=0
+
+IPI_SRC_CPU=0
+
+helpme() {
+    printf "Usage: %s [-h] [-todg args]
+	[-h <help>]
+	[-s <source cpu for ipi test> (default: 0)]
+	[-m <location of the module>]
+	[-o <location of the output>]
+	[-v <verbose> (execute test across all CPU threads)]
+	[-i <run timer tests>]
+	\n" "$0"
+    exit 2
+}
+
+cpu_is_online() {
+    local cpu=$1
+    if [ ! -f "/sys/devices/system/cpu/cpu$cpu/online" ]; then
+        printf "CPU %s: file not found: /sys/devices/system/cpu/cpu%s/online" "$cpu" "$cpu"
+        return 0
+    fi
+    status=$(cat /sys/devices/system/cpu/cpu"$cpu"/online)
+    return "$status"
+}
+
+check_valid_cpu() {
+    local cpu="$1"
+    local cpu_count
+
+    cpu_count="$(nproc)" # Get the number of CPUs on the system
+
+    if [[ "$cpu" =~ ^[0-9]+$ ]]; then
+        if ((cpu >= 0 && cpu < cpu_count)); then
+            cpu_is_online "$cpu"
+            online_status=$?
+            if [ "$online_status" -eq "1" ]; then
+                return 1
+            else
+                printf "CPU %s is offline." "$cpu"
+                return 0
+            fi
+        fi
+    fi
+    return 0
+}
+
+parse_arguments() {
+    while getopts ht:m:s:o:vt:it: arg; do
+        case $arg in
+        h) # --help
+            helpme
+            ;;
+        m) # --mod-file
+            MODULE=$OPTARG
+            ;;
+        s) #
+            IPI_SRC_CPU=$OPTARG
+            check_valid_cpu "$IPI_SRC_CPU"
+            cpu_status=$?
+            if [ "$cpu_status" == "0" ]; then
+                printf "%s is an invalid CPU. Exiting.." "$IPI_SRC_CPU"
+                exit
+            fi
+            ;;
+        o) # output log files
+            LOG=$OPTARG
+            ;;
+        v) # verbose mode - execute tests across all CPU threads
+            VERBOSE=1
+            ;;
+        i) # run timer tests
+            RUN_TIMER_TEST=1
+            ;;
+        \?)
+            helpme
+            ;;
+        esac
+    done
+}
+
+ins_mod() {
+    debugfs_file=/sys/kernel/debug/powerpc/latency_test/ipi_latency_ns
+    # Check if the module is already loaded
+    if [ -f "$debugfs_file" ]; then
+        printf "Module %s already loaded\n\n" "$MODULE"
+        return 0
+    fi
+    # Try to load the module
+    if [ ! -f "$MODULE" ]; then
+        printf "%s module does not exist. Exiting\n" "$MODULE"
+        exit $ksft_skip
+    fi
+    printf "Inserting %s module\n\n" "$MODULE"
+    insmod "$MODULE"
+    if [ $? != 0 ]; then
+        printf "Insmod %s failed\n" "$MODULE"
+        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))
+}
+
+# Perform operation on each CPU for the given state
+# $1 - Operation: enable (0) / disable (1)
+# $2 - State to enable
+op_state() {
+    for ((cpu = 0; cpu < NUM_CPUS; cpu++)); do
+        cpu_is_online "$cpu"
+        local cpu_status=$?
+        if [ "$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_state_information() {
+    for ((state = 0; state < NUM_STATES; state++)); do
+        state_name=$(cat /sys/devices/system/cpu/cpu"$IPI_SRC_CPU"/cpuidle/state"$state"/name)
+        state_name_arr+=("$state_name")
+    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/cpu"$IPI_SRC_CPU"/cpuidle/state"$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<=$2; i++)printf "%s%s",i,ORS;next} 1' RS=, FS=-
+}
+
+extract_core_information() {
+    declare -a thread_arr
+    for ((cpu = 0; cpu < NUM_CPUS; cpu++)); do
+        cpu_is_online "$cpu"
+        local cpu_status=$?
+        if [ "$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+=("$cpu")
+            continue
+        fi
+        element_in "${sib_arr[0]}" "${thread_arr[@]}"
+        if [ $? == 0 ]; then
+            continue
+        fi
+        core_arr+=("${sib_arr[0]}")
+
+        for thread in "${sib_arr[@]}"; do
+            thread_arr+=("$thread")
+        done
+    done
+
+    src_siblings=$(cat /sys/devices/system/cpu/cpu"$IPI_SRC_CPU"/topology/thread_siblings_list)
+    for c in $(parse_cpuset "$src_siblings"); do
+        first_core_arr+=("$c")
+    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=$!
+        # Wait for the workload to achieve 100% CPU usage
+        sleep 1
+    fi
+    taskset -c "$IPI_SRC_CPU" echo "$dest_cpu" >/sys/kernel/debug/powerpc/latency_test/ipi_cpu_dest
+    ipi_latency=$(cat /sys/kernel/debug/powerpc/latency_test/ipi_latency_ns)
+    src_cpu=$(cat /sys/kernel/debug/powerpc/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
+    printf "...IPI Latency Test...\n" | tee -a "$LOG"
+
+    printf "...Baseline IPI Latency measurement: CPU Busy...\n" >>"$LOG"
+    printf "%s %10s %12s\n" "SRC_CPU" "DEST_CPU" "IPI_Latency(ns)" >>"$LOG"
+    for cpu in "${core_arr[@]}"; do
+        cpu_is_online "$cpu"
+        local cpu_status=$?
+        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 "${avg_arr[@]}"
+    printf "Baseline Avg IPI latency(ns): %s\n" "$avg" | tee -a "$LOG"
+
+    for ((state = 0; state < NUM_STATES; state++)); do
+        unset avg_arr
+        printf "...Enabling state: %s...\n" "${state_name_arr[$state]}" >>"$LOG"
+        cpuidle_enable_state $state
+        printf "%s %10s %12s\n" "SRC_CPU" "DEST_CPU" "IPI_Latency(ns)" >>"$LOG"
+        for cpu in "${core_arr[@]}"; do
+            cpu_is_online "$cpu"
+            local cpu_status=$?
+            if [ "$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 "${avg_arr[@]}"
+        printf "Expected IPI latency(ns): %s\n" "${latency_arr[$state]}" >>"$LOG"
+        printf "Observed Avg IPI latency(ns) - State %s: %s\n" "${state_name_arr[$state]}" "$avg" | tee -a "$LOG"
+        cpuidle_disable_state $state
+    done
+}
+
+# Extract the residency in microseconds and convert to nanoseconds.
+# Add 200 ns so that the timer stays for a little longer than the residency
+extract_residency() {
+    for ((state = 0; state < NUM_STATES; state++)); do
+        residency=$(($(cat /sys/devices/system/cpu/cpu"$IPI_SRC_CPU"/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" sleep 1
+    taskset -c "$dest_cpu" echo "$3" >/sys/kernel/debug/powerpc/latency_test/timeout_expected_ns
+    # Wait for the result to populate
+    sleep 0.1
+    timeout_diff=$(cat /sys/kernel/debug/powerpc/latency_test/timeout_diff_ns)
+    src_cpu=$(cat /sys/kernel/debug/powerpc/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
+    printf "\n...Timeout Latency Test...\n" | tee -a "$LOG"
+
+    printf "...Baseline Timeout Latency measurement: CPU Busy...\n" >>"$LOG"
+    printf "%s %10s\n" "Wakeup_src" "Baseline_delay(ns)" >>"$LOG"
+    for cpu in "${core_arr[@]}"; do
+        cpu_is_online "$cpu"
+        local cpu_status=$?
+        if [ "$cpu_status" == 0 ]; then
+            continue
+        fi
+        timeout_test_once "baseline" "$cpu" "$TIMEOUT"
+        printf "%-3s %13s\n" "$src_cpu" "$timeout_diff" >>"$LOG"
+        avg_arr+=("$timeout_diff")
+    done
+    compute_average "${avg_arr[@]}"
+    printf "Baseline Avg timeout diff(ns): %s\n" "$avg" | tee -a "$LOG"
+
+    for ((state = 0; state < NUM_STATES; state++)); do
+        unset avg_arr
+        printf "...Enabling state: %s...\n" "${state_name_arr["$state"]}" >>"$LOG"
+        cpuidle_enable_state "$state"
+        printf "%s %10s\n" "Wakeup_src" "Delay(ns)" >>"$LOG"
+        for cpu in "${core_arr[@]}"; do
+            cpu_is_online "$cpu"
+            local cpu_status=$?
+            if [ "$cpu_status" == 0 ]; then
+                continue
+            fi
+            timeout_test_once "test" "$cpu" "$TIMEOUT"
+            printf "%-3s %13s\n" "$src_cpu" "$timeout_diff" >>"$LOG"
+            avg_arr+=("$timeout_diff")
+        done
+        compute_average "${avg_arr[@]}"
+        printf "Expected timeout(ns): %s\n" "${residency_arr["$state"]}" >>"$LOG"
+        printf "Observed Avg timeout diff(ns) - State %s: %s\n" "${state_name_arr["$state"]}" "$avg" | tee -a "$LOG"
+        cpuidle_disable_state "$state"
+    done
+}
+
+# Function to exit the test if not intended
+exit_test() {
+    printf "Exiting the test. Test not intended to run.\n"
+    exit "$ksft_skip"
+}
+
+printf "Running this test enables all CPU idle states by the time it concludes.\n"
+printf "Note: This test does not restore previous idle state.\n"
+
+declare -a residency_arr
+declare -a latency_arr
+declare -a core_arr
+declare -a first_core_arr
+declare -a state_name_arr
+
+parse_arguments "$@"
+
+rm -f "$LOG"
+touch "$LOG"
+
+NUM_CPUS=$(nproc --all)
+NUM_STATES=$(ls -1 /sys/devices/system/cpu/cpu"$IPI_SRC_CPU"/cpuidle/ | wc -l)
+
+extract_core_information
+extract_state_information
+
+ins_mod "$MODULE"
+
+run_ipi_tests
+if [ "$RUN_TIMER_TEST" == "1" ]; then
+    run_timeout_tests
+fi
+
+# Enable all idle states for all CPUs
+op_cpuidle $ENABLE
+printf "Removing %s module\n" "$MODULE"
+printf "Full Output logged at: %s\n" "$LOG"
+
+if [ -f "$MODULE" ]; then
+    rmmod "$MODULE"
+fi
+
+exit "$exit_status"
diff --git a/tools/testing/selftests/powerpc/cpuidle_latency/settings b/tools/testing/selftests/powerpc/cpuidle_latency/settings
new file mode 100644
index 000000000000..e7b9417537fb
--- /dev/null
+++ b/tools/testing/selftests/powerpc/cpuidle_latency/settings
@@ -0,0 +1 @@
+timeout=0
-- 
2.25.1

Re: [RFC v2 1/2] powerpc/cpuidle: cpuidle wakeup latency based on IPI and timer events

[Srikar Dronamraju]

* Aboorva Devarajan <aboorvad@linux.vnet.ibm.com> [2023-08-28 11:45:29]:

> From: Pratik R. Sampat <psampat@linux.ibm.com>
> 
> Introduce a mechanism to fire directed IPIs from a source CPU to a
> specified target CPU and measure the time incurred on waking up the
> target CPU in response.
> 
> Also, introduce a mechanism to queue a hrtimer on a specified CPU and
> subsequently measure the time taken to wakeup the CPU.
> 
> Define a simple debugfs interface that allows for adjusting the
> settings to trigger IPI and timer events on a designated CPU, and to
> observe the resulting cpuidle wakeup latencies.
> 
> Signed-off-by: Pratik R. Sampat <psampat@linux.ibm.com>
> Signed-off-by: Aboorva Devarajan <aboorvad@linux.vnet.ibm.com>
> Reviewed-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com>
> ---
>  arch/powerpc/Kconfig.debug                 |  10 ++
>  arch/powerpc/kernel/Makefile               |   1 +
>  arch/powerpc/kernel/test_cpuidle_latency.c | 156 +++++++++++++++++++++
>  3 files changed, 167 insertions(+)
>  create mode 100644 arch/powerpc/kernel/test_cpuidle_latency.c
> 
> diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
> index 2a54fadbeaf5..e175fc3028ac 100644
> --- a/arch/powerpc/Kconfig.debug
> +++ b/arch/powerpc/Kconfig.debug
> @@ -391,3 +391,13 @@ config KASAN_SHADOW_OFFSET
>  	default 0xe0000000 if PPC32
>  	default 0xa80e000000000000 if PPC_BOOK3S_64
>  	default 0xa8001c0000000000 if PPC_BOOK3E_64
> +
> +config CPUIDLE_LATENCY_SELFTEST
> +	tristate "Cpuidle latency selftests"
> +	depends on CPU_IDLE
> +	help
> +	  Provides a kernel module that run tests using the IPI and
> +	  timers to measure cpuidle latency.
> +
> +	  Say M if you want these self tests to build as a module.
> +	  Say N if you are unsure.
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index 2919433be355..3205ecbd9d8f 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -87,6 +87,7 @@ obj-$(CONFIG_PPC_WATCHDOG)	+= watchdog.o
>  obj-$(CONFIG_HAVE_HW_BREAKPOINT)	+= hw_breakpoint.o
>  obj-$(CONFIG_PPC_DAWR)		+= dawr.o
>  obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_ppc970.o cpu_setup_pa6t.o
> +obj-$(CONFIG_CPUIDLE_LATENCY_SELFTEST)  += test_cpuidle_latency.o

This line is now introduced in between CONFIG_PPC_BOOK3S_64 objects.
May be its better this was added such that CONFIG_PPC_BOOK3S_64 objects
are all together.

>  obj-$(CONFIG_PPC_BOOK3S_64)	+= cpu_setup_power.o
>  obj-$(CONFIG_PPC_BOOK3S_64)	+= mce.o mce_power.o
>  obj-$(CONFIG_PPC_BOOK3E_64)	+= exceptions-64e.o idle_64e.o
> diff --git a/arch/powerpc/kernel/test_cpuidle_latency.c b/arch/powerpc/kernel/test_cpuidle_latency.c
> new file mode 100644
> index 000000000000..3c3c119389c1
> --- /dev/null
> +++ b/arch/powerpc/kernel/test_cpuidle_latency.c
> @@ -0,0 +1,156 @@
> +// 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;

NIT: The above line could have been part of the declaration itself.

> +	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 hrtimer_callback(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);

No need to break the above line.

> +	timer_wakeup.timer.function = hrtimer_callback;
> +	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;
> +}
> +
> +/*
> + * Send a directed IPI from the current CPU (source) to the destination CPU and
> + * measure the latency on wakeup.
> + */
> +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;
> +}
> +
> +/* Queue a hrtimer on a specified desitination CPU and measure the time taken to
> + * wakeup the CPU.
> + */
> +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", arch_debugfs_dir);
> +	if (!dir) {
> +		pr_alert("latency_test: failed to create /sys/kernel/debug/powerpc/latency_test\n");
> +		return -1;
> +	}
> +	temp = debugfs_create_file("ipi_cpu_dest", 0644, dir, NULL, &ipi_ops);
> +	if (!temp) {
> +		pr_alert("latency_test: failed to create /sys/kernel/debug/powerpc/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", 0644, dir, NULL, &timeout_ops);
> +	if (!temp) {
> +		pr_alert("latency_test: failed to create /sys/kernel/debug/powerpc/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");
> -- 
> 2.25.1
> 
Otherwise looks good to me.

Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

-- 
Thanks and Regards
Srikar Dronamraju