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[82.212.34.85]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48fe4c88e5asm45150915e9.6.2026.05.15.01.24.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 15 May 2026 01:24:52 -0700 (PDT) Date: Fri, 15 May 2026 10:24:51 +0200 Message-ID: <32dea9123588227a02971341b22e84d3.tomge68@gmail.com> From: Tom Gebhardt To: Qais Yousef Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Vincent Guittot Subject: Re: [PATCH v2 00/13] sched/fair/schedutil: Better manage system response time In-Reply-To: <20260515014250.tueinbuk7ldttdop@airbuntu> References: <20260504020003.71306-1-qyousef@layalina.io> <20260515014250.tueinbuk7ldttdop@airbuntu> Content-Type: text/plain; charset=UTF-8 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Hi Qais, Thanks for the follow-up. Here are the patch isolation results and answers to your questions. Regarding the governor: Yes, I'm running `ondemand`, not `schedutil`. My mistake for not mentioning that upfront - I assumed the improvement was due to the util_est path being triggered regardless of the governor. The improvement is clearly measurable even with `ondemand`, which is surprising given that your patches specifically target `schedutil`. Patch isolation -- 12/13 only vs. both: I re-ran the benchmarks with patch 13/13 (`sched/pelt: Always allow load updates`) reverted, keeping only patch 12/13 (`sched/fair: Call update_util_est() after dequeue_entities()`). Results using stress-ng 0.15.06 pipe stressor (4 workers, 20s): Kernel Clock pipe bogo ops/s delta vs. 6.6 ----------------------------------- -------- ---------------- ------------- 6.6.78-v8-16k+ 2400 MHz 2 129 330 +/-0% (ref) 6.6.78-v8-16k+ 2800 MHz 2 487 746 +/-0% (ref) 7.0.0-v8-16k+ stock 2400 MHz 1 694 011 -20.5% 7.0.0-v8-16k+ stock 2800 MHz 1 851 567 -25.6% 7.0.0 + ttwu only (10 patches) 2400 MHz 1 836 006 -13.8% 7.0.0 + ttwu only (10 patches) 2800 MHz 1 934 076 -22.3% 7.0.0 + ttwu + patch 12/13 only 2400 MHz 2 054 879 -3.5% 7.0.0 + ttwu + patch 12/13 only 2800 MHz 2 415 617 -2.9% 7.0.0 + ttwu + patches 12+13 2400 MHz 1 996 002 -6.3% 7.0.0 + ttwu + patches 12+13 2800 MHz 2 342 144 -5.9% The key finding: patch 12/13 alone outperforms the combined set on ARM. Adding patch 13/13 actually hurts performance slightly -- about 3 percentage points -- at both clock speeds. This suggests that `sched/pelt: Always allow load updates` has a negative interaction on ARM/Cortex-A76, possibly related to how PELT decay is handled without `schedutil` active, or an ARM-specific DELAY_DEQUEUE interaction. Patch 12/13 alone closes the gap to just -2.9% vs. 6.6 at 2800 MHz (OC), and -3.5% at nominal 2400 MHz. That is a remarkable recovery from the -31.9% regression in 7.0 stock. Regarding Perfetto traces: Unfortunately I cannot provide sched-analyzer traces at this time -- the kernel is not compiled with CONFIG_DEBUG_INFO_BTF=y (pahole/dwarves not available in this build environment), which is required for BPF CO-RE. I can try to arrange that for a future run if it would still be useful. Device: Raspberry Pi 5 (8 GB, C1-stepping), Bookworm arm64, kernel rpi-7.0.y. Background: https://github.com/raspberrypi/linux/issues/7308 Tom