From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 3CF91606A330 for ; Wed, 4 Nov 2026 12:31:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=j+JjsJAY Received: by kanga.kvack.org (Postfix) id 3DF6F6B00EF; Wed, 4 Nov 2026 07:31:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3B6DF6B05B1; Wed, 4 Nov 2026 07:31:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2CE376B05B4; Wed, 4 Nov 2026 07:31:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 055DB6B00EF for ; Wed, 4 Nov 2026 07:31:40 -0500 (EST) Received: from smtpin07.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 59E931205D3 for ; Wed, 4 Nov 2026 12:31:40 +0000 (UTC) X-FDA: 85397372760.07.9393CAC Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf12.hostedemail.com (Postfix) with ESMTP id BC1994000B for ; Wed, 4 Nov 2026 12:31:38 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=j+JjsJAY; spf=pass (imf12.hostedemail.com: domain of frederic@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1793795498; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=d7N3s/Fk0FC0DIJXDd2TXVzu86yiov/bVF/UpU5EDxA=; b=Fpkyz8t/EJTSh/dsk4MPJUZTT49BEnEqQOJ7hlUeO2i20kgHgrCN/KB2nnhP/97nwji5Ss EN0YkOokSfrqyG5acS9mZaop4FDI8KgcA7Tyr/UDRjU/L4I26MtOq0vYpaUzS681FJMFkY xfHESvILBQNkq9OMBkOF/dxfyjtTZyI= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1793795498; b=vMmsge3p05yC+46HUH3OP37jiJgz7zNc6W45yjcs1ZZObO0GgWZytbBdrxr6IrFOIMbPD9 ON0SNTVZ6TfjS2pvCn1J3+j9xLGJ3j1K8aktKs81npylfNtpiyAiiKQG89eJPZXOrYH2KY nNP8pv+m0sbX8C8Lj1ZQFGQN1xuEHQs= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=j+JjsJAY; spf=pass (imf12.hostedemail.com: domain of frederic@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 4B35060F32; Wed, 4 Nov 2026 12:31:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7B9431F000C1; Wed, 4 Nov 2026 12:31:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793795498; bh=d7N3s/Fk0FC0DIJXDd2TXVzu86yiov/bVF/UpU5EDxA=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=j+JjsJAYkPpZEw11dLp/jNcSe2cW7ZtaW501/o17Jebog2qcBPsZHeT2iz62r2ae1 WLk4RorrJUNOZk1wfUVtX0q/D2494vTsgA6m1EkyzcnRqumKVl5JkWhU/xmkSy6WqX OOdehNRcyKKe4Wzk6WK50t2c7/27ovl2oC8hmpafP6aCD5rDynipvmry4fIUcYmpb2 tD0bdg5ktq+JKFY1K90H6FiBXm3qP5N7gf+YBI/gFda4CBZvVyPyG/wEgdhShr+/OI xBB8dE+rAHcXcTnvsv+xYB4B9Vz8KDFpbsWF3dJxEfs64gbpZIUL1iT/IV5GQp1yRM bqcbnsNEabvcw== Date: Wed, 4 Nov 2026 13:31:35 +0100 From: Frederic Weisbecker To: Waiman Long Cc: Matthew Ruffell , Tejun Heo , Peter Zijlstra , Ingo Molnar , Andrew Morton , David Hildenbrand , Caron Wills , Ridong Chen , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Jay Vosburgh Subject: Re: [PATCH 2/6] kthread: Keep unbound kthreads off nohz_full CPUs Message-ID: References: <20261103075940.110308-1-matthew.ruffell@canonical.com> <20261103075940.110308-3-matthew.ruffell@canonical.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam06 X-Stat-Signature: 818oxs69g9rffmm1rpdsrc13u6hzjfbw X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Queue-Id: BC1994000B X-Rspam-User: X-HE-Tag: 1793795498-167280 X-HE-Meta: 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 Pd4LgZ5N WCH68mOr4RDBz2vbCK65jKnbauwfEwzNYc3CZTJc8gSF+JFaOD/3CerIPGjbmdvqTYYz0Y8+t7CmBaLrjXMdzM5TjOHel4s/OoqgifDmbLOcMGrjVu+0fEf4jK7LawhSq+5na4g0rwLpzDtfcz2k1ZBjWUrHaJXniFodNexmnouT7w+UKwgFmeBNo7wG1k4MB9x4/KjsKjhM3A4doOG3eyeHp73+M8INujbzJ8spIfT6Ndmpk3PGmX60sCTvXdsVQArAXsfjpyicxjCBftSdiPXhog+5Bgg7XzyeYxMNRm9F1nxNjTN/L8cG0Yet8GsDwktZ/r8Tr+FB2gI8RqjA7Nl3QUu3aWH0y6wzR Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 Le Tue, Nov 03, 2026 at 10:13:38AM -0500, Waiman Long a écrit : > On 11/3/26 9:01 AM, Frederic Weisbecker wrote: > > Le Tue, Nov 03, 2026 at 08:59:36PM +1300, Matthew Ruffell a écrit : > > > From: Caron Wills > > > > > > Since commit 041ee6f3727a ("kthread: Rely on HK_TYPE_DOMAIN for > > > preferred affinity management") kthread_fetch_affinity() only removes > > > domain isolated CPUs from a kthread's affinity, assuming that nohz_full > > > CPUs are always domain isolated as well. Up to v6.13 every kthread > > > inherited kthreadd's affinity to housekeeping_cpumask(HK_TYPE_KTHREAD), > > > and from v6.14 the preferred affinity was filtered with HK_TYPE_KTHREAD, > > > so nohz_full CPUs were always excluded. > > This was done on purpose because on all setup we have met so far, it didn't > > make sense to run nohz_full with load balancing. After all the point is to > > run a pinned single task on a single CPU. We have seen too many misconfigured > > CPU isolation workloads due to that constraint not being enforced since the > > origins. > > > > I'm open to counter-arguments of course but you better have a good case. > > I do see configurations where nohz_full/managed_irq CPUs are set at boot > time without isolcpus=domain. But these nohz_full CPUs are there as a backup > in case some latency critical workloads need a set of fully isolated CPUs to > run on. Sure. > Right now, isolcpus=domain can be set dynamically by using the > cpuset isolated partition feature and they will be used when the need > arises. Exactly. Whathever way you use to do domain isolation. -- Frederic Weisbecker SUSE Labs