From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 CAD3521CC58; Wed, 8 Jul 2026 18:20:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783534856; cv=none; b=R3/gDKo+mnSxYUCJouCfN3WqSnEJLsV4CYnfAK7NFYOkC6D9XuMYO8p/JgbI72QCmw2vjX0aPoxCFXhZahlAXWKc9YA/8b1qJcVQUNc23h5YOFfPdD470fq34FPsA2xt0UjzaDryguzbgv4qEzm6kF1iQ2jgByZpvKGfctMnrdA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783534856; c=relaxed/simple; bh=cvmz4hrqphk7KcxE6scMvQxStY1tVz3nneCeb9HEoB0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=PqELRc66+tDTRIgmwhTl0FdttzIJ6zEgMwfDLOp52H0UDtxAB8G1HHlJFUCAD02Gmo/vGFSpHH+s0b2n1VFxluk9w1kbjeU2/VlGOlvOWTUWgmwtFax4jegCkvq+tVrmRbulKZoxiTrTROhhqYrSvuwp2fCZdKHF/3L24WFdatc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XH1Rugh7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XH1Rugh7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 21D6F1F000E9; Wed, 8 Jul 2026 18:20:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783534855; bh=xqQF5csxL2bubvNMLTUkN6CATUyeRMaGUkO45vk4Qps=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=XH1Rugh7zd6INp3CuIv2M+2JfyqyfxGQvezLDVvr9aiLvLIQA/wa+VeLv+ghqPaJ/ TuI0vb1b4+Aj2gJi9VdxlvteFPkccxCU8pIKzmjxWMAF49w0pXn/sAGsFAnGTAPx/2 rCbwseJgjA2FCN4l0x4+U/ziEt5zDSEQCNTmCE3162Qrbik9Y6RzKkCx55ESZgRTHo KNbDqryFWEnhmDsvIlFJ5dSamdV0HDuENvV3K5LP42Yd6Emf9C5zWn/ocqBD3NLysl Ys1JgeeVjr1nMQhqj9Ho2gaSBo5/jdEgfi665LnZjuIB9nccDlonfD++2vBKd6Zc4C /rkat9LFNQCDQ== Date: Wed, 8 Jul 2026 08:20:54 -1000 From: Tejun Heo To: Andrea Righi Cc: David Vernet , Changwoo Min , sched-ext@lists.linux.dev, Emil Tsalapatis , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 sched_ext/for-7.3 25/36] sched_ext: Add the SCX_CAP_ENQ_IMMED cap Message-ID: References: <20260707001229.1410929-1-tj@kernel.org> <20260707001229.1410929-26-tj@kernel.org> 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Hello, Andrea. On Wed, Jul 08, 2026 at 03:06:36PM +0200, Andrea Righi wrote: ... > I bisected it and this was to be the offending commit. > > IIUC, what's happening is that qmap grants the child CPUs 2–3, but race-sched > stressor can pin its tasks to CPU 1. Since the child has no enqueue capability > there, the tasks repeatedly land on the reject DSQ and eventually trigger the > RCU stall. > > Maybe we need a forced fallback when a task's affinity mask has no active CPU on > which its scheduler holds SCX_CAP_BASE? > > Checking this only during sched_setaffinity() won't work because capabilities > can be revoked after the affinity change succeeds. What do you think? Yeah, I should have mentioned in the head message but there are still a few missing pieces for full support. Two big ones: - cgroup migrations don't move the tasks across schedulers as they should. - No fallback mechanism when a sub-sched doesn't have any CPUs for some of its tasks. So, after this series, things mostly work as long as tasks don't move across cgroup boundaries and tasks in sub-scheds aren't affined to the cpus tha the sub-sched doesn't have access to. Will update the head message. I haven't decided on the details yet but it's most likely going to be reserving some time slice off from the root sched to run the tasks w/o cpu access. Thanks. -- tejun