5.4-stable review patch. If anyone has any objections, please let me know.
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From: Gautham R. Shenoy gautham.shenoy@amd.com
[ 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 --- tools/power/cpupower/utils/idle_monitor/mperf_monitor.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c b/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c index 0e8c0b879d4b..09c606760464 100644 --- a/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c +++ b/tools/power/cpupower/utils/idle_monitor/mperf_monitor.c @@ -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;