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 91B79CDB474 for ; Fri, 20 Oct 2023 16:25:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1377756AbjJTQZq (ORCPT ); Fri, 20 Oct 2023 12:25:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38148 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1377814AbjJTQZp (ORCPT ); Fri, 20 Oct 2023 12:25:45 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 075801A8 for ; Fri, 20 Oct 2023 09:25:42 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE901C433C8; Fri, 20 Oct 2023 16:25:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1697819142; bh=UP9gGnH+TMdepTYQpqbOnkkE8UJZHaoe0fFcfivPJXA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=o+IuCMzFvhxtIx2NYnuc80RdD4Ae4RyQeD2dXvfhJtBivw/VeSML7krktd3dPs8Kx StkJT61SLa8OJ4o3i9o/yTI6QwxE61m4YOZ44+cTDhpGe5Gx50Th6P949Bg8lzbyf8 knTg1e1YNcHosgJ/r8wJXvNbhfXeYpgR09uu9WVWvvlkO9DOgLoe9FA8BB/iVpUShw 5WW4Mq737K/s1WvDP+Sy6rurGWoMQ4EvUykEGM9dxN/tkBzJmuwBFQIeupxhI1MBMH 6Q7DjWq5SocQyZGW5OYq2AxtKcg0BnUuu+HvePyKvBdpCmjbmgg6SBIuKKid47d1A+ QVQYQ8lUUUXyg== Date: Fri, 20 Oct 2023 10:25:39 -0600 From: Keith Busch To: Bart Van Assche Cc: Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org, "Martin K . Petersen" , Ming Lei , Damien Le Moal , Yu Kuai , Ed Tsai Subject: Re: [PATCH] block: Improve shared tag set performance Message-ID: References: <20231018180056.2151711-1-bvanassche@acm.org> <20231020044159.GB11984@lst.de> <0d2dce2a-8e01-45d6-b61b-f76493d55863@acm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0d2dce2a-8e01-45d6-b61b-f76493d55863@acm.org> Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Fri, Oct 20, 2023 at 09:17:11AM -0700, Bart Van Assche wrote: > On 10/19/23 21:41, Christoph Hellwig wrote: > > On Wed, Oct 18, 2023 at 11:00:56AM -0700, Bart Van Assche wrote: > > > Note: it has been attempted to rework this algorithm. See also "[PATCH > > > RFC 0/7] blk-mq: improve tag fair sharing" > > > (https://lore.kernel.org/linux-block/20230618160738.54385-1-yukuai1@huaweicloud.com/). > > > Given the complexity of that patch series, I do not expect that patch > > > series to be merged. > > > > Work is hard, so let's skip it? That's not really the most convincing > > argument. Hey, I'm the biggest advocate for code improvement by code > > removal, but you better have a really good argument why it doesn't hurt > > anyone. > > Hi Christoph, > > No, it's not because it's hard to improve the tag fairness algorithm > that I'm proposing to skip this work. It's because I'm convinced that > an improved fairness algorithm will have a negative performance impact > that is larger than that of the current algorithm. > > Do you agree that the legacy block layer never had any such fairness > algorithm and also that nobody ever complained about fairness issues > for the legacy block layer? I think that's a strong argument in favor of > removing the fairness algorithm. The legacy block request layer didn't have a tag resource shared among multiple request queues. Each queue had their own mempool for allocating requests. The mempool, I think, would always guarantee everyone could get at least one request.