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[2620:137:e000::1:20]) by mx.google.com with ESMTP id c68-20020a624e47000000b00640d906a8f3si2603491pfb.245.2023.05.09.08.42.47; Tue, 09 May 2023 08:43:02 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@suse.cz header.s=susede2_rsa header.b=yuE+aeDK; dkim=neutral (no key) header.i=@suse.cz header.s=susede2_ed25519 header.b=U9lDf+k2; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235101AbjEIO7i (ORCPT + 99 others); Tue, 9 May 2023 10:59:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59284 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229998AbjEIO7g (ORCPT ); Tue, 9 May 2023 10:59:36 -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 623B83A8D; Tue, 9 May 2023 07:59:33 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (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 077C021C74; Tue, 9 May 2023 14:59:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1683644372; 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=Ws2pfb2I14kNmCpwcuY6Ln1HcgD90lj/eSZsutM5HBc=; b=yuE+aeDKrScwEsnGm+ZyOwiNY9Lt+wu1e/s8mXUWFd+2M4Vb9RGil2L9BEOsZ7MWTFYHVZ dvfXesG20+SnDBzMjkDBMyJTeFMvW0f4vzjbzGhaHle+8wI7zxCF7Q+iKVG4FeuQigKK/Y iRbWXri2yo3XxWAawAi2zMRqHuXjc7I= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1683644372; 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=Ws2pfb2I14kNmCpwcuY6Ln1HcgD90lj/eSZsutM5HBc=; b=U9lDf+k2G3IdMfweOC+bN8zhFCLOyeCzlW4MnzmWE4CRq0KZUCd7YpDsZ1eJWHI0lq4KaK DvZSWyLP+UcRy1Bg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (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 imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 9A66A13581; Tue, 9 May 2023 14:59:31 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id B+iCItNfWmQ9HgAAMHmgww (envelope-from ); Tue, 09 May 2023 14:59:31 +0000 Date: Tue, 9 May 2023 16:53:32 +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: <20230509145332.GA32559@twin.jikos.cz> Reply-To: dsterba@suse.cz References: <20230509015032.3768622-1-tj@kernel.org> <20230509015032.3768622-9-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230509015032.3768622-9-tj@kernel.org> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Spam-Status: No, score=-3.7 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_SOFTFAIL,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 08, 2023 at 03:50:27PM -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. > > WHAT TO LOOK FOR > ================ > > The conversions are from > > alloc_workqueue(WQ_UNBOUND | flags, 1, args..) > > to > > alloc_ordered_workqueue(flags, args...) > > which don't cause any functional changes. If you know that fully ordered > execution is not ncessary, please let me know. I'll drop the conversion and > instead add a comment noting the fact to reduce confusion while conversion > is in progress. > > If you aren't fully sure, it's completely fine to let the conversion > through. The behavior will stay exactly the same and we can always > reconsider later. > > As there are follow-up workqueue core changes, I'd really appreciate if the > patch can be routed through the workqueue tree w/ your acks. Thanks. > > v3: btrfs_alloc_workqueue() excluded again. The concurrency level of a > workqueue allocated through btrfs_alloc_workqueue() may be dynamically > adjusted through thresh_exec_hook(), so they can't be ordered. > > v2: btrfs_alloc_workqueue() updated too as suggested by Wang. > > Signed-off-by: Tejun Heo > Cc: Wang Yugui > Cc: Chris Mason > Cc: Josef Bacik > Cc: David Sterba > Cc: linux-btrfs@vger.kernel.org > --- > fs/btrfs/disk-io.c | 2 +- > fs/btrfs/scrub.c | 6 ++++-- > 2 files changed, 5 insertions(+), 3 deletions(-) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index 59ea049fe7ee..32d08aed88b6 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -2217,7 +2217,7 @@ static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info) > fs_info->qgroup_rescan_workers = > btrfs_alloc_workqueue(fs_info, "qgroup-rescan", flags, 1, 0); > fs_info->discard_ctl.discard_workers = > - alloc_workqueue("btrfs_discard", WQ_UNBOUND | WQ_FREEZABLE, 1); > + alloc_ordered_workqueue("btrfs_discard", WQ_FREEZABLE); > > if (!(fs_info->workers && fs_info->hipri_workers && > fs_info->delalloc_workers && fs_info->flush_workers && I think there are a few more conversions missing. There's a local flags variable in btrfs_init_workqueues 2175 static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info) 2176 { 2177 u32 max_active = fs_info->thread_pool_size; 2178 unsigned int flags = WQ_MEM_RECLAIM | WQ_FREEZABLE | WQ_UNBOUND; And used like 2194 fs_info->fixup_workers = 2195 btrfs_alloc_workqueue(fs_info, "fixup", flags, 1, 0); 2213 fs_info->qgroup_rescan_workers = 2214 btrfs_alloc_workqueue(fs_info, "qgroup-rescan", flags, 1, 0); WQ_UNBOUND is not mentioned explicitliy like for the "btrfs_discard" workqueue. Patch v2 did the switch in btrfs_alloc_workqueue according to the max_active/limit_active parameter but this would affect all queues and not all of them require to be ordered. In btrfs_resize_thread_pool the workqueue_set_max_active is called directly or indirectly so this can set the max_active to a user-defined mount option. Could this be a problem or trigger a warning? This would lead to max_active==1 + WQ_UNBOUND.