From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=90.155.50.34 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794048217; b=eUMmA2ZCKKBw4gkJN6CK+tacNMfJz9D2DO7Egx1Tig1Nd/7+7EzpUOBL0iDO7Wn353wl R5Q+EvfMyQIlI3ktbCFZCG5iGhnX2Bc8fU/VxyOsfcKEL7Jj8j79Z4DlizVwSFYoe9PBV Fv2VDKQK5ubIfAG9Ab/tQSNz9pbcIfzqjPNz9G6pcLog71O6R6abARSXofkdUlXB2hbNq m2PmP0oPAqD3lL4woapXvddzXGhf9SjIOGCl68ueZGC+rYZHI4Ol2IjzOtpsfkMorcBtW Yl7BU15Jm8Wn0g5DPtz8RTbiVyArlgkHunjbbN+tv8DBWqhHxS4ccRsA0s9UvJtGwXQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794048217; h=DMARC-Filter:DKIM-Signature:Received:Received:Date:From:To:Cc: Subject:Message-ID:References:MIME-Version:Content-Type: Content-Disposition:In-Reply-To; bh=00YgSuh+6jx0afSBDldxTfJk1blWDnLXe0VtLaUOxXk=; b=tGTE0tuDU1QULm1ovuXFImvl35dIHMOxYQfjFRgcCVd1mLEhf5vHfEOHXkakrymRQWJf SgvLyJAjnP9rTdXGNKzIeEMQIxNzFDo4Pj3kElq+GKi8PV9dV2mMbf6RYIEt4INddbMG6 oV79KtVDrNxZWiGIVoNIn/MOa1LXqiEjFlv7p5Z+nPZ4FTQ0PZ/PJYZ6CdlDvjLaJuxaF RmjME8znKVAMlrRdMHNUDS536FqGErMuPj1iIQnrauEdSbFGKv4rXH4qvvC3SRicHaRNO Sqx3BMkzK42Uz4/OI7gXzeGP2yGPFLDAFUDjyAwDUOvtPRA3okKk3Zf88/7Qjk1saeA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=WQ4vEdpT; arc=none smtp.remote-ip=90.155.50.34 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90950606A330; Sat, 7 Nov 2026 10:43:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 90950606A330 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.a=rsa-sha256 header.s=casper.20170209 header.b=WQ4vEdpT DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=00YgSuh+6jx0afSBDldxTfJk1blWDnLXe0VtLaUOxXk=; b=WQ4vEdpTpZXUFp0gPkIKkOjiXH VhxJd/x7V53CLfavcaj/BKuDXIlOYi4f5cqfDTgde17E0rGlk40dJjy/zZ2pcBrbtT+Up9sZ9JM2D U9j5jfgF87PiMz53RVu5GqY+VT0IS7bYVriiRRcWwYxAZLAkclp2nnyuoSV3YuteoBMiY8v5eLu8G SpKd3Av0YjIYGyW1yZgo45Did2Hjp5V1RhD1PC/AupJNJKjFFlUtsN0orQ0gqDpLd3opKLbZbyWgi IKH+AOlK2V80w4EKi+NEpSit9SP1vhwEfi7Blwv+LdrOMbP3ko14dF0jh9zqrB5/Ztt1mD/LHOdKQ cJl17gUA==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.100.1 #2 (Red Hat Linux)) id 1xPdtS-0000000Gido-3xDF; Sat, 07 Nov 2026 10:43:31 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id B8FE4300339; Sat, 07 Nov 2026 11:43:29 +0100 (CET) Date: Sat, 7 Nov 2026 11:43:29 +0100 From: Peter Zijlstra To: Steven Rostedt Cc: Mathieu Desnoyers , tglx@kernel.org, mingo@redhat.com, linux-kernel@vger.kernel.org, will@kernel.org, boqun@kernel.org, longman@redhat.com, bigeasy@linutronix.de, clrkwllms@kernel.org, dvhart@infradead.org, dave@stgolabs.net, andrealmeid@igalia.com, shuah@kernel.org, juri.lelli@redhat.com, linux-rt-devel@lists.linux.dev, linux-kselftest@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/5] locking/rtmutex: Stop spinning on the owner when the waiter is woken Message-ID: <20261107104329.GA2668564@noisy.programming.kicks-ass.net> References: <20261106235931.1478800-1-mathieu.desnoyers@efficios.com> <20261106235931.1478800-2-mathieu.desnoyers@efficios.com> <20261107002927.3cbad7ff@fedora> 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261107002927.3cbad7ff@fedora> On Sat, Nov 07, 2026 at 12:29:27AM -0500, Steven Rostedt wrote: > On Fri, 6 Nov 2026 18:59:27 -0500 > Mathieu Desnoyers wrote: > > > The top waiter of an rt_mutex spins while the owner runs, > > rtmutex_spin_on_owner(), and does not stop when it is woken: its timeout > > and a signal find it running, set it TASK_RUNNING, and the spin goes on > > until the owner leaves its CPU or the waiter's own CPU has to > > reschedule. A PI futex owner is a user task that may run as long as it > > likes. On v7.4-rc1, in 8-CPU VMs, behind an owner spinning in userspace, > > a 1ms pthread_mutex_timedlock() returns ETIMEDOUT 126ms to 631ms late on > > average, 1.4s at most, a SIGUSR1 is handled up to 1.9s late, and a > > waiter killed with SIGKILL is reaped 0.5s late on average. With > > PREEMPT_RT the wound of a ww_mutex is missed the same way: two contexts > > in an ABBA on two CPUs at SCHED_FIFO spin on each other, and the older > > one gets its second lock after 96ms on average, 0.95s at most. > > > > The above is very verbose. Are you starting to use AI? ;-) He definitely is. I can't read the above, its word soup. Part of using AI is making sure the Changelog is actually readable. This is not.