From: Vincent Guittot vincent.guittot@linaro.org
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 (cherry picked from commit e37617c8e53a1f7fcba6d5e1041f4fd8a2425c27) --- kernel/sched/cpufreq_schedutil.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c index cfe7c625d2ad..819ec1ccc08c 100644 --- a/kernel/sched/cpufreq_schedutil.c +++ b/kernel/sched/cpufreq_schedutil.c @@ -156,7 +156,11 @@ 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); }
/**