Re: [PATCH v2 2/2] selftest/cpuidle: Add support for cpuidle latency measurement

Hi Pratik,


On Fri, Jul 17, 2020 at 02:48:01PM +0530, Pratik Rajesh Sampat wrote:

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 <redacted>

A few comments below.

---
 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

[..skip..]

+
+ins_mod()
+{
+	if [ ! -f "$MODULE" ]; then
+		printf "$MODULE module does not exist. Exitting\n"

If the module has been compiled into the kernel (due to a
localyesconfig, for instance), then it is unlikely that we will find
it in /lib/modules. Perhaps you want to check if the debugfs
directories created by the module exist, and if so, print a message
saying that the modules is already loaded or some such?

+		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))

It would be good to assert that "size" isn't 0 here.

+}
+
+# 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

So, on offlined CPUs, we won't see
/sys/devices/system/cpu/cpu$cpu/cpuidle/state$state directory. You
should probably perform this operation only on online CPUs.

+		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

Ditto

+	done
+}

This is a helper function. For better readability of the main code you
can define the following wrappers and use them.


cpuidle_enable_state()
{
	state=$1
	op_state 1 $state
}

cpuidle_disable_state()
{
	state=$1
	op_state 0 $state

}

+

[..snip..]

+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

If a CPU is offline, then we should skip it here.

+				# 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

Again only perform this on online CPUs.

+		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

Ditto.

+			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
+}
+

--
Thanks and Regards
gautham.