Commit 1b5c6a60 authored Jun 12, 2025 by Gautham R. Shenoy Committed by Greg Kroah-Hartman Aug 28, 2025

pm: cpupower: Fix the snapshot-order of tsc,mperf, clock in mperf_stop()

[ Upstream commit cda7ac8ce7de84cf32a3871ba5f318aa3b79381e ]

In the function mperf_start(), mperf_monitor snapshots the time, tsc
and finally the aperf,mperf MSRs. However, this order of snapshotting
in is reversed in mperf_stop(). As a result, the C0 residency (which
is computed as delta_mperf * 100 / delta_tsc) is under-reported on
CPUs that is 100% busy.

Fix this by snapshotting time, tsc and then aperf,mperf in
mperf_stop() in the same order as in mperf_start().

Link: https://lore.kernel.org/r/20250612122355.19629-2-gautham.shenoy@amd.com


Signed-off-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent c41fef8b

tools/power/cpupower/utils/idle_monitor/mperf_monitor.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -201,9 +201,9 @@ static int mperf_stop(void)
		int cpu;

		for (cpu = 0; cpu < cpu_count; cpu++) {
		mperf_measure_stats(cpu);
		mperf_get_tsc(&tsc_at_measure_end[cpu]);
		clock_gettime(CLOCK_REALTIME, &time_end[cpu]);
		mperf_get_tsc(&tsc_at_measure_end[cpu]);
		mperf_measure_stats(cpu);
		}

		return 0;