From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 68DAF366079 for ; Fri, 8 May 2026 12:09:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778242163; cv=none; b=Ij+TGPo04bJ8SoErkUkaEvMN2Yl0mIr9GjXuPGi9KclaarS2c7QrvFkc76TnU8uKnYUdGFI+0x5pn9i9/w6hwoCWEjw9am/nW7TZVlOJpBXwFaEgH2P0RS6e83yrfQIhvUI0FMO2PaIuMi9lsxVSYPAa4YhE8RKUgkzuLJRMXGo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778242163; c=relaxed/simple; bh=jTJiUrv8M0vlVxXeJA73u/70vXctrJec85bjrbHhujg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=c5HMEG5ZYTWpMRTDvij944e9UaxDV7Ktgljrwm73GLEKWGt0iGC0aT+t4oAHtYBtaGf8RxyNpb243aVR4VGICNFbljs8RyKSP3U8BB0lPCLvbvZTwv9sQeBhJUsrFXjTDrMwzmGdGQMKWhqgKdg/Py4Xpn3Df9gOxN/Wha99PpU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XJJAMBXO; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="XJJAMBXO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 00C83C2BCB8; Fri, 8 May 2026 12:09:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778242163; bh=jTJiUrv8M0vlVxXeJA73u/70vXctrJec85bjrbHhujg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XJJAMBXOfvCDspu4N9952hDAcuwFpZ8I+V5GHPViKwdvX+/vm8WeNaUfi+DgKPP2z /gPKvmCRscfbHaT4wAZGhXbzZ6jN2ddR1sZmSNiLC6E1yCdpcZpK3wdMFgrL9i+QSP bZteSGA6Qssxn/ry430LgLGLju+XnAigNwJKHToPcbxFQcNKeqElDPhA41T3pZVUOe 0Bnphppx3xYPh0hiYn3Eh3mLpVkiWV/D7bUo1Fl5CBmll8AU8UVXbei1bBChN+/+ep zMPTAV76h1UomvZZRHRNI8PpNxlzNMoh1+a7xg8gnUQAx1ZJkuXEfw/7/HnsXMDFtN +sq/RTCjAIZLA== Date: Fri, 8 May 2026 14:09:20 +0200 From: Frederic Weisbecker To: Tejun Heo Cc: Marco Crivellari , Breno Leitao , linux-kernel@vger.kernel.org, Lai Jiangshan , Sebastian Andrzej Siewior , Michal Hocko Subject: Re: [RFC PATCH 0/2] Add queue_*() functions and prefer per-cpu workqueue and flag Message-ID: References: <20260505161658.401998-1-marco.crivellari@suse.com> 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: Le Thu, May 07, 2026 at 11:27:52AM -1000, Tejun Heo a écrit : > > Anyhow, this idea is based on customer reports I've seen previously. > > We noticed that with certain workloads, specific per-cpu work creates > > noise on isolated CPUs. With a flag like that we can identify which > > workqueues prefer to be per-cpu and *not* for correctness. This allows > > using a boot parameter / sysctl, for example, to keep those workqueues > > affined only to housekeeping CPUs. > > > > Of course, if we can achieve the same with a system workqueue (like > > system_prefer_percpu_wq), that would also be fine. I think it would be > > way easier, it should be similar to what we're doing with > > system_power_efficient_wq [1]. > > WQ_AFFN_CPU is more flexible as the tasks aren't pinned to the CPU but there > may be downsides: > > - Concurrency management isn't available. > > - Would create more kworkers. > > Maybe the original plan can be adapted to: > > - Add WQ_PERFER_PERCPU as discussed before. > > - At boot time, allow selecting whether to back them with percpu wqs or > WQ_AFFN_X unbound ones. Maybe we can even experiment with default to > WQ_AFFN_CPU. Isn't WQ_POWER_EFFICIENT enough for what we want here? ie: it does a per-cpu preference except when some config is enabled or isolation is on. It could be renamed to WQ_PREFER_PERCPU to generalize its meaning for more than just power purposes. Thanks. -- Frederic Weisbecker SUSE Labs