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Wed, 04 Nov 2026 14:06:42 -0800 (PST) Received: from fedora ([2.35.201.240]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b56fca22f4sm24879935e9.13.2026.11.04.14.06.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 14:06:41 -0800 (PST) From: Francesco Nigro To: Mike Galbraith Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , K Prateek Nayak , Mario Limonciello , Huang Rui , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Subject: Re: [REPORT] sched: ITMT + DELAY_DEQUEUE: woken task waits ~1 ms behind another task on the preferred CPU while allowed CPUs are idle Date: Wed, 4 Nov 2026 23:06:22 +0100 Message-ID: <20261104220622.3542344-1-nigro.fra@gmail.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <32db09358aecb92c55c8c1295fa71b6a73306999.camel@gmx.de> References: <20261103154603.1893325-1-nigro.fra@gmail.com> <25edb6cd36cb77b82b40826b97232438f1443516.camel@gmx.de> <20261103233352.2282883-1-nigro.fra@gmail.com> <32db09358aecb92c55c8c1295fa71b6a73306999.camel@gmx.de> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Wed, 2026-11-04 at 04:13 +0100, Mike Galbraith wrote: > In your specific case, dunno. In general, absolutely. I checked with boost on too, on the same box and kernel. I ran asym_min and tbench on CPUs 4-7, without SMT siblings, with clocks pinned and boost off, and with boost on and the full frequency range, DELAY_DEQUEUE on. With boost on, 0.82-1.09 % of asym_min wakeups per run waited at least 0.5 ms with ITMT on, and none with ITMT off. tbench throughput was the same with ITMT on or off in every setting (within 1 %), and so was the busy CPUs' clock (within 0.2 %). According to these new runs, with boost on ITMT gives no throughput advantage and still causes the long stalls. As a side note, I agree about DELAY_DEQUEUE: disabling it reduced tbench throughput at full load, with ITMT on or off. Scripts and raw output: https://github.com/franz1981/itmt-delay-dequeue-repro/tree/1400f15 Tool use as in the report. Thanks, Franz