From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9CC1CF459E5 for ; Fri, 10 Apr 2026 22:11:40 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7FA2F6B0089; Fri, 10 Apr 2026 18:11:39 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7D2446B008A; Fri, 10 Apr 2026 18:11:39 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6E7E56B0092; Fri, 10 Apr 2026 18:11:39 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 601E66B0089 for ; Fri, 10 Apr 2026 18:11:39 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 212891401A3 for ; Fri, 10 Apr 2026 22:11:39 +0000 (UTC) X-FDA: 84644043918.26.F7E3B3B Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf24.hostedemail.com (Postfix) with ESMTP id 65F95180008 for ; Fri, 10 Apr 2026 22:11:37 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=O0UosEhb; spf=pass (imf24.hostedemail.com: domain of dgc@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=dgc@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=1775859097; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=aEKxRds2gv9nUcHds3kAu8Ord4mdUMqS/yDW0rbJ/Ls=; b=mHTMYzD12BFgqkNMbvg7lGmzD80MQQHpoLT51i6Md+383sZSVn3iyN5h/utlyVNzgYUUvm Q7OytMHAOhBq63UJevd1CmjVTBsQeUisuZlJJS6Xywf6nKzK1NLCPa+A9xb2fNdF1G9PKC jDdiloJSrQIJshP8BnKNT1b8GD8u1qM= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1775859097; a=rsa-sha256; cv=none; b=nkHXlrFMou+2sGVhetMQRw0QPIn2SNxcKOZpT/mUdyYGI+6mk0efK4yRZaCs/HM7VbT5Kk 0aEGyZGGr6Uv1yk3KnghbzMV5wDkwCqQhI6UiSZ3tHkaM4QC7yrqlAPxohKshk8Net2Hxw MdNahFj+3Iri9+30YN7vcJuvaHp+ptw= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=O0UosEhb; spf=pass (imf24.hostedemail.com: domain of dgc@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=dgc@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 25BE243EF7; Fri, 10 Apr 2026 22:11:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E95A7C19421; Fri, 10 Apr 2026 22:11:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775859096; bh=TD1pp2xHcOkkxrulkbwy4Mz16Cdc52MMGL5vPeTdYro=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O0UosEhbQqlCe7BDoVNDV3AAplB6buy82yLtBbVNnnDFVUUmLlktsZGxSpAoXukfp wg1EIi9X11ZYxQzJt+naoFnVDbC8YqcVZc5uyk6Lg4jGRboGTOl0xyYiBcfKSiXrSX i8INWnE/Lr/xlyPLe4tg9PR00Z6MKMbbRAguYJEgxGJMFQDd8umIhR7xsUkrC/ckqI 4kCoTEqkNhYcllyJ7ox0GBi8C17YtPK56RfylOTPVuWtaipiKEoorhZeOTt4dHuWi0 6QF5oGJStzdnDSv6MuqFkn3Evysc8l/uOygH1vfAc8tuVOPFHMm/bhALTHFkYrjjvC tYHcWc5zFAfGQ== Date: Sat, 11 Apr 2026 08:11:22 +1000 From: Dave Chinner To: Christoph Hellwig Cc: Tal Zussman , Jens Axboe , "Matthew Wilcox (Oracle)" , Christian Brauner , "Darrick J. Wong" , Carlos Maiolino , Al Viro , Jan Kara , Bart Van Assche , Gao Xiang , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 8/8] RFC: use a TASK_FIFO kthread for read completion support Message-ID: References: <20260409160243.1008358-1-hch@lst.de> <20260409160243.1008358-9-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260409160243.1008358-9-hch@lst.de> X-Rspamd-Queue-Id: 65F95180008 X-Stat-Signature: 77xdx7i5k3zy6ckkgcfoo449beuyo5n1 X-Rspam-User: X-Rspamd-Server: rspam07 X-HE-Tag: 1775859097-100016 X-HE-Meta: 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 Ph3J3IBN WApwsniRtDfegs/231h6w2hr5IfgQblCU+Zqxk+M6pZhi3PuAKElOwGnNKwKesoaPv6WrcA0gwR7UZpIpufpCMkmVjS53JFy7WycQuBQN6o8pQ/xvnWok7KheBFc1dxaKhhw/XfDhBxykrrOYwfIvsGaGmAacKVk3fIb8IyR2RNduk1YeG9HfZugG2IviPIwpvNd7JfRoWuPxTWJFLIitq/QwhRFHRk5fwHlznymqOl6vDBklYp3KuMUemjFVLNclkG9gd5hNV655Cb6D4hphEv7gxKzJZIOQJbYIwSAsoOMM/mBAKMjKsq6el5ffGqv09Vma Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 09, 2026 at 06:02:21PM +0200, Christoph Hellwig wrote: > Commit 3fffb589b9a6 ("erofs: add per-cpu threads for decompression as an > option") explains why workqueue aren't great for low-latency completion > handling. Switch to a per-cpu kthread to handle it instead. This code > is based on the erofs code in the above commit, but further simplified > by directly using a kthread instead of a kthread_work. > > Signed-off-by: Christoph Hellwig Can we please not go back to the (bad) old days of individual subsystems needing their own set of per-cpu kernel tasks just sitting around idle most of of the time? The whole point of the workqueue infrastructure was to get rid of this widely repeated anti-pattern. If there's a latency problem with workqueue scheduling, then we should be fixing that problem rather than working around it in every subsystem that thinkgs it has a workqueue scheduling latency issue... -Dave. -- Dave Chinner dgc@kernel.org