On Sat, Aug 16, 2025 at 01:01:44AM +0800, Wentao Guan wrote:

From ddd3f1ed6e88d88502d2b42e159ac976b4194b78 Mon Sep 17 00:00:00 2001 From: Vincent Guittot vincent.guittot@linaro.org Date: Sun, 14 Jan 2024 19:36:00 +0100 Subject: [PATCH] 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 (cherry picked from commit e37617c8e53a1f7fcba6d5e1041f4fd8a2425c27) Signed-off-by: Wentao Guan guanwentao@uniontech.com

---

I tested the patch two days ago, and the upstream commit can be directly apply.

---

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 cfe7c625d2ad6..819ec1ccc08cf 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);

} /**

Does not apply against the latest 6.6.y kernel release :(

thanks,

greg k-h