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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D74E0C77B7A for ; Fri, 26 May 2023 12:58:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243513AbjEZM6R (ORCPT ); Fri, 26 May 2023 08:58:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229579AbjEZM6P (ORCPT ); Fri, 26 May 2023 08:58:15 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B11EF114; Fri, 26 May 2023 05:58:13 -0700 (PDT) Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id 6A2FA21B38; Fri, 26 May 2023 12:58:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1685105892; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=CpDq1pEfvg+8XPmzv2uGKWtOfWpZEnVao4Y2FaBvNdM=; b=YG7Y03GVSMFb8q+Rg9XvSvo0mxcRYM+dU3uIw9PH9ZqThWYg3B+EczCjikkCWC4kujTYnb 6gVef3hKq0LAmCK+pXea7PRXfSrv5BCrAvFiW2roPa+OBTwSJIbL3nAJY+DCLvAuM7vdMx +ynLi3q42MQVvCy8v3bZ4jO36YV7shE= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1685105892; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=CpDq1pEfvg+8XPmzv2uGKWtOfWpZEnVao4Y2FaBvNdM=; b=hPceyvtQa2/Lf0ouJIMCpNaAMz5QTN9fZMjhDJcDTXh9oHvgI5ccWu8ylX7gm1LDWKBe6w sGsYZ0dSQCcgj/Bg== Received: from imap1.suse-dmz.suse.de (imap1.suse-dmz.suse.de [192.168.254.73]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap1.suse-dmz.suse.de (Postfix) with ESMTPS id 1FCF013684; Fri, 26 May 2023 12:58:12 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id 29dDBuSscGTiXgAAGKfGzw (envelope-from ); Fri, 26 May 2023 12:58:12 +0000 Date: Fri, 26 May 2023 14:52:03 +0200 From: David Sterba To: Tejun Heo Cc: jiangshanlai@gmail.com, linux-kernel@vger.kernel.org, kernel-team@meta.com, Wang Yugui , Chris Mason , Josef Bacik , David Sterba , linux-btrfs@vger.kernel.org Subject: Re: [PATCH 08/13] btrfs: Use alloc_ordered_workqueue() to create ordered workqueues Message-ID: <20230526125203.GA14830@suse.cz> Reply-To: dsterba@suse.cz References: <20230509015032.3768622-1-tj@kernel.org> <20230509015032.3768622-9-tj@kernel.org> <20230509145332.GA32559@twin.jikos.cz> <20230509233620.GN32559@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 25, 2023 at 01:33:08PM -1000, Tejun Heo wrote: > BACKGROUND > ========== > > When multiple work items are queued to a workqueue, their execution order > doesn't match the queueing order. They may get executed in any order and > simultaneously. When fully serialized execution - one by one in the queueing > order - is needed, an ordered workqueue should be used which can be created > with alloc_ordered_workqueue(). > > However, alloc_ordered_workqueue() was a later addition. Before it, an > ordered workqueue could be obtained by creating an UNBOUND workqueue with > @max_active==1. This originally was an implementation side-effect which was > broken by 4c16bd327c74 ("workqueue: restore WQ_UNBOUND/max_active==1 to be > ordered"). Because there were users that depended on the ordered execution, > 5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered") > made workqueue allocation path to implicitly promote UNBOUND workqueues w/ > @max_active==1 to ordered workqueues. > > While this has worked okay, overloading the UNBOUND allocation interface > this way creates other issues. It's difficult to tell whether a given > workqueue actually needs to be ordered and users that legitimately want a > min concurrency level wq unexpectedly gets an ordered one instead. With > planned UNBOUND workqueue updates to improve execution locality and more > prevalence of chiplet designs which can benefit from such improvements, this > isn't a state we wanna be in forever. > > This patch series audits all callsites that create an UNBOUND workqueue w/ > @max_active==1 and converts them to alloc_ordered_workqueue() as necessary. > > BTRFS > ===== > > * fs_info->scrub_workers initialized in scrub_workers_get() was setting > @max_active to 1 when @is_dev_replace is set and it seems that the > workqueue actually needs to be ordered if @is_dev_replace. Update the code > so that alloc_ordered_workqueue() is used if @is_dev_replace. > > * fs_info->discard_ctl.discard_workers initialized in > btrfs_init_workqueues() was directly using alloc_workqueue() w/ > @max_active==1. Converted to alloc_ordered_workqueue(). > > * fs_info->fixup_workers and fs_info->qgroup_rescan_workers initialized in > btrfs_queue_work() use the btrfs's workqueue wrapper, btrfs_workqueue, > which are allocated with btrfs_alloc_workqueue(). > > btrfs_workqueue implements automatic @max_active adjustment which is > disabled when the specified max limix is below a certain threshold, so > calling btrfs_alloc_workqueue() with @limit_active==1 yields an ordered > workqueue whose @max_active won't be changed as the auto-tuning is > disabled. > > This is rather brittle in that nothing clearly indicates that the two > workqueues should be ordered or btrfs_alloc_workqueue() must disable > auto-tuning when @limit_active==1. > > This patch factors out the common btrfs_workqueue init code into > btrfs_init_workqueue() and add explicit btrfs_alloc_ordered_workqueue(). > The two workqueues are converted to use the new ordered allocation > interface. > > Signed-off-by: Tejun Heo > Cc: Wang Yugui > Cc: Chris Mason > Cc: Josef Bacik > Cc: David Sterba > Cc: linux-btrfs@vger.kernel.org > --- > Hello, > > David, I think this is a bit too invasive to carry through workqueue tree. > If this looks okay, can you plase apply route it through the btrfs tree? Yesd and I actually prefer to take such patches via btrfs tree unless there's a strong dependency on other patches from another subsystem. Thanks.