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 E921BC77B75 for ; Fri, 21 Apr 2023 05:05:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232255AbjDUFFM (ORCPT ); Fri, 21 Apr 2023 01:05:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59668 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230134AbjDUFFG (ORCPT ); Fri, 21 Apr 2023 01:05:06 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D28A730DF for ; Thu, 20 Apr 2023 22:05:04 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 7467060DB5 for ; Fri, 21 Apr 2023 05:05:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65813C433EF; Fri, 21 Apr 2023 05:05:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1682053503; bh=zyiQTQNWEDkw/+8pCYnYVPA8sw2qiEl9H3N9Y/qAMsw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IXdrpuQ2VlQYfto28X1B7/CrJdriB1DT6JaocXOrVCfN6zSaWZ8cvUvXrJKm4XN03 Oz3w4bJvC2baMhMiZorCUAo259r/3/bKgLivyzf6u9t2wqhzuXKg9MXCJh7V1etFdH kQTAkQce6l9mG6mVtRHLhk5h8L3xw/muIDZyf4GU= Date: Fri, 21 Apr 2023 07:03:30 +0200 From: Greg Kroah-Hartman To: Tejun Heo Cc: jiangshanlai@gmail.com, linux-kernel@vger.kernel.org, kernel-team@meta.com, Fei Li Subject: Re: [PATCH 13/22] virt: acrn: Use alloc_ordered_workqueue() to create ordered workqueues Message-ID: References: <20230421025046.4008499-1-tj@kernel.org> <20230421025046.4008499-14-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230421025046.4008499-14-tj@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 20, 2023 at 04:50:37PM -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. > > Signed-off-by: Tejun Heo > Cc: Fei Li > Cc: Greg Kroah-Hartman > --- > drivers/virt/acrn/ioreq.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Acked-by: Greg Kroah-Hartman