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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-485188923c2sm40345475e9.14.2026.03.04.01.54.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Mar 2026 01:54:17 -0800 (PST) Date: Wed, 4 Mar 2026 09:54:15 +0000 From: David Laight To: Peter Zijlstra Cc: Yafang Shao , mingo@redhat.com, will@kernel.org, boqun@kernel.org, longman@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, mark.rutland@arm.com, mathieu.desnoyers@efficios.com, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [RFC PATCH 1/2] locking: add mutex_lock_nospin() Message-ID: <20260304095415.4d5f2528@pumpkin> In-Reply-To: <20260304090249.GN606826@noisy.programming.kicks-ass.net> References: <20260304074650.58165-1-laoar.shao@gmail.com> <20260304074650.58165-2-laoar.shao@gmail.com> <20260304090249.GN606826@noisy.programming.kicks-ass.net> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 4 Mar 2026 10:02:49 +0100 Peter Zijlstra wrote: > On Wed, Mar 04, 2026 at 03:46:49PM +0800, Yafang Shao wrote: > > Introduce mutex_lock_nospin(), a helper that disables optimistic spinning > > on the owner for specific heavy locks. This prevents long spinning times > > that can lead to latency spikes for other tasks on the same runqueue. > > This makes no sense; spinning stops on need_resched(). > That might still be an issue if a high priority process is spinning. But a %sys spike doesn't imply a latency spike. Is this using the osq_lock.c code? That will have problems on overprovisioned VMs, it tries to find out whether the hypervisor has switched out - but ISTR that is flawed. In reality a spin lock shouldn't be held for long enough to cause any kind latency issue. So something in the code that reads the list of filter functions needs to be done differently so that the lock isn't held for as long. David