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 178AC3AC0D7 for ; Fri, 20 Mar 2026 12:50:04 +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=1774011007; cv=none; b=PB9ubrlCv1/maTWFMlxkHt1nEmXzwGcnBk79dhEa50HYRvmAAp8gZb5tySs6Dzel2/ffqxihASA4PwdI66YGxC2CB5lXVPAPVyva89dU4XqsyRAqIw5JryNqdGH5xJIErTQ6yTjhLzHUD2YeVyi7d9RDJZCFi4Aq7BsT1wjFA7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774011007; c=relaxed/simple; bh=02D6wOjKp4d1K22Sc39bK+qvk2Uyx53PyByVHHwEkJQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=etpOaIME+EdjIbNuuzrtQTn3v+nqLY2nYTwZWghsJ2p+gl/NyvmzHjJ5Ao8MHPuRPH6iiGrGlA6xfWcjW9GPgVo8mtEWjtxwslT56BBnwGIUxv7h2uK/yPYyzaVR2pejsO4efFjTFIce+TQw45+ZtyUPV7MRgyF/1RgImgCAlT0= 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=v+S7Ay+S; 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="v+S7Ay+S" 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=cQC1O3UPvRUYoigNPPSf3RgohKruUrMjFYfjVLQN58Y=; b=v+S7Ay+SO0Qy/YP0FqIGRjrVmT kBmrcQdqYPTC6cwa1GNwCRaDMzi9GrxJyYHIeDcBZrknqhTwO19tVzUKtsDQOiRG4nThlS9ihZJWE up3dJcDVIl9tJcJHfqMqT9bKac/ayBmEinvmJ+ey+ntExm4p+Akw/pNwDmvmTumTCv7+lZW0WBKui VM9IL3mP2M6NQod5GPdTJbV2kjr90V1tUaiifjnoDX3iWQp+PU7mwgr9L/0Nm1pBZLSGI/cWpOE5E EoXd/3gebfRWQCrGz1HFgSZA8aPtynGetZrdbpX5P0z1xw7MEZwCVivRgSwGie87nvqd4/6hg0pZr ocn7Tz8g==; 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 1w3ZIg-00000007mdf-39M7; Fri, 20 Mar 2026 12:50:02 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 2EAEB300578; Fri, 20 Mar 2026 13:50:02 +0100 (CET) Date: Fri, 20 Mar 2026 13:50:02 +0100 From: Peter Zijlstra To: Pan Deng Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, tianyou.li@intel.com, tim.c.chen@linux.intel.com, yu.c.chen@intel.com Subject: Re: [PATCH v2 0/4] sched/rt: mitigate root_domain cache line contention Message-ID: <20260320125002.GH3739106@noisy.programming.kicks-ass.net> References: <20260320095955.GQ3738786@noisy.programming.kicks-ass.net> 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-Disposition: inline In-Reply-To: <20260320095955.GQ3738786@noisy.programming.kicks-ass.net> On Fri, Mar 20, 2026 at 10:59:55AM +0100, Peter Zijlstra wrote: > On Mon, Jul 21, 2025 at 02:10:22PM +0800, Pan Deng wrote: > > When running multi-instance FFmpeg workload in cloud environment, > > cache line contention is severe during the access to root_domain data > > structures, which significantly degrades performance. > > > > The SUT is a 2-socket machine with 240 physical cores and 480 logical > > What's a SUT? > > > CPUs. 60 FFmpeg instances are launched, each pinned to 4 physical cores > > (8 logical CPUs) for transcoding tasks. Sub-threads use RT priority 99 > > with FIFO scheduling. FPS(frame per second) is used as score. > > So I think we can do some of this, but that workload is hilariously > poorly configured. > > You're pinning things but not partitioning, why? If you would have > created 60 partitions, one for each FFmpeg thingy, then you wouldn't > have needed any of this. > > You're running at FIFO99 (IOW prio-0) and then claiming prio-0 is used > more heavily than others... will d0h. What priority assignment scheme > led to this? Is there a sensible reason these must be 99? > Also, you failed the most basic of tasks, Cc all the relevant people. I would've hoped at least some of the 'reviewer' you had would've told you about that. Notably, Steve is the one that often looks after this RT stuff.