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| author | Vincent Guittot <vincent.guittot@linaro.org> | 2024-01-14 19:36:00 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2024-01-16 10:41:25 +0100 |
| commit | e37617c8e53a1f7fcba6d5e1041f4fd8a2425c27 (patch) | |
| tree | bfdc57da1b74f2a0e53812c919cba61f1f2decd5 /kernel/sched | |
| parent | bfe8eb3b85c571f7e94e1039f59b462505b8e0fc (diff) | |
| download | linux-e37617c8e53a1f7fcba6d5e1041f4fd8a2425c27.tar.gz linux-e37617c8e53a1f7fcba6d5e1041f4fd8a2425c27.tar.bz2 linux-e37617c8e53a1f7fcba6d5e1041f4fd8a2425c27.zip | |
sched/fair: Fix frequency selection for non-invariant case
Linus reported a ~50% performance regression on single-threaded
workloads on his AMD Ryzen system, and bisected it to:
9c0b4bb7f630 ("sched/cpufreq: Rework schedutil governor performance estimation")
When frequency invariance is not enabled, get_capacity_ref_freq(policy)
is supposed to return the current frequency and the performance margin
applied by map_util_perf(), enabling the utilization to go above the
maximum compute capacity and to select a higher frequency than the current one.
After the changes in 9c0b4bb7f630, the performance margin was applied
earlier in the path to take into account utilization clampings and
we couldn't get a utilization higher than the maximum compute capacity,
and the CPU remained 'stuck' at lower frequencies.
To fix this, we must use a frequency above the current frequency to
get a chance to select a higher OPP when the current one becomes fully used.
Apply the same margin and return a frequency 25% higher than the current
one in order to switch to the next OPP before we fully use the CPU
at the current one.
[ mingo: Clarified the changelog. ]
Fixes: 9c0b4bb7f630 ("sched/cpufreq: Rework schedutil governor performance estimation")
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Bisected-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Wyes Karny <wkarny@gmail.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Wyes Karny <wkarny@gmail.com>
Link: https://lore.kernel.org/r/20240114183600.135316-1-vincent.guittot@linaro.org
Diffstat (limited to 'kernel/sched')
| -rw-r--r-- | kernel/sched/cpufreq_schedutil.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index 95c3c097083e..eece6244f9d2 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -133,7 +133,11 @@ unsigned long get_capacity_ref_freq(struct cpufreq_policy *policy) if (arch_scale_freq_invariant()) return policy->cpuinfo.max_freq; - return policy->cur; + /* + * Apply a 25% margin so that we select a higher frequency than + * the current one before the CPU is fully busy: + */ + return policy->cur + (policy->cur >> 2); } /** |