From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 54C352F12DA for ; Thu, 23 Apr 2026 08:04:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776931502; cv=none; b=un4At0AMNfnGeKw5W75Ya/GppB3SYwGTBSShIbOiBzqXKIO7EK2PecyusIGqF4NPVRqLEFvIH1Duay7EE5DpELV0Ms0mS6zwQcAMENui5h3fuy1zDvYOhZ3ow+/LqDeUX68GKZ7sBfZ924zKIsNYQ3BMW61RksO0aFWvuo54lyM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776931502; c=relaxed/simple; bh=qOsCh2KLfr2D8t+7w8Ytu2zXWZzxg9qyFbhCAskgbMs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TFWDHsO0KkSDNdxEbsrCeAtt/9XMatU5Px8R5Qd1bcFWWmVzmB0zbxAXdV/YWK18qpmBvOvrHoPhb5IeoL/5ukywa+HXrN7wbVALGs743PS8w3w6Ti8eZ+x0WO7NBUemLV/Zv3fm2BtJu5I7S6i+BRi8xkAjXEL7OyZ3cxo9et8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=RKfAmFQ6; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="RKfAmFQ6" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=cWAQr1IwXd5ucKZpMUFHRMFd08NEGpmiplIThRL2lxk=; b=RKfAmFQ6dA0S5wubC0UI9vkq97 If6v5TO0wxx4HIzRE8hfmPg9D2IT6UgoLqaFAj2ZqGXsTQjZENn1dSNF2gsvhmzBIx3Bud89xfFwO ityOH303+DOe2RMxtpE/nhUJ2QAo5b1+2D9JP3GIgs1gEjAwHW8wV6B80MUrNXtdSA1+zA/uuJi6O uX/pdX+0hS10mldwA9L0BjE1pjuPG9SLnMSwPAylyjC2GEoPFxFi6hC3j8KpUcldMzE3TG3eUm0+L OTzixXXMde2k4r7gKOjgzvpa+c8G1OUrKdwdHX4cCzXs4ynuKBeWT+tcEl4v9fE4I6BIpTx+jReJj Jih+qrNA==; 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 4.98.2 #2 (Red Hat Linux)) id 1wFp3P-0000000D5MV-13Jg; Thu, 23 Apr 2026 08:04:55 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 693253008E2; Thu, 23 Apr 2026 10:04:53 +0200 (CEST) Date: Thu, 23 Apr 2026 10:04:53 +0200 From: Peter Zijlstra To: Mike Galbraith Cc: Tom Gebhardt , mingo@redhat.com, linux-kernel@vger.kernel.org Subject: Re: sched/fair: DELAY_DEQUEUE causes ~25% pipe IPC regression on Raspberry Pi 5 Message-ID: <20260423080453.GQ3126523@noisy.programming.kicks-ass.net> References: <2877d886d8470f4ea3393e8c2e570a059c2b8b1b.camel@gmx.de> <0a93288ace2a95616066f7a26cc45d6407dc5147.camel@gmx.de> <8f02df669230c771cb34aec704e287d9ef2efa6a.camel@gmx.de> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8f02df669230c771cb34aec704e287d9ef2efa6a.camel@gmx.de> On Thu, Apr 23, 2026 at 06:51:20AM +0200, Mike Galbraith wrote: > On Tue, 2026-04-21 at 05:55 +0200, Mike Galbraith wrote: > > On Mon, 2026-04-20 at 12:59 +0200, Tom Gebhardt wrote: > > > > > > > Would you be willing to run the 6.6 comparison with stress-ng 0.15.06 > > > on your Pi 5? > > > > No need, your reported DELAY_DEQUEUE impact for 6.12.75+rpt-rpi-2712 > > appeared with stress-ng 0.15.06. > > > > However, my local 6.12.y branch kernel, which has all eevdf fixes as > > well as Peter's still pending sched/ttwu series, still does NOT repro. > > > > git@homer:..git/raspberrypi-kernel> quilt applied|grep delay > > patches/eevdf/WIP/0043-sched-fair-Removed-unsued-cfs_rq.h_nr_delayed.patch > > patches/eevdf/WIP/0047-sched-fair-Do-not-try-to-migrate-delayed-dequeue-task.patch           <== ? > > patches/eevdf/WIP/0065-sched-Change-ttwu_runnable-vs-sched_delayed.patch > > patches/eevdf/WIP/0066-sched-Add-ttwu_queue-support-for-delayed-tasks.patch > > patches/eevdf/WIP/0089-sched-fair-Prevent-negative-lag-increase-during-delayed-dequeue.patch <== ? > > I've finally finished slogging through my quilt backport battery, and > my dinky/cute rpi5 asserts that what prevents the local heavily patched > rpi-6.12-y@6.12.81 kernel from reproducing has nothing to do with > pointed at suspects, rather Peter's long pending ttwu series is > entirely responsible. Humm, I'd almost forgotten about that. I suppose I'll have to go dust that off again.