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

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[ 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>
This commit is contained in:
Gautham R. Shenoy 2025-06-12 17:53:54 +05:30 • committed by Greg Kroah-Hartman
commit 1b5c6a600f
1 changed files with 2 additions and 2 deletions
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4
tools/power/cpupower/utils/idle_monitor/mperf_monitor.c
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@ -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;