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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C471CC00449 for ; Wed, 3 Oct 2018 13:25:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97C46213A2 for ; Wed, 3 Oct 2018 13:25:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97C46213A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.cz Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726971AbeJCUOV (ORCPT ); Wed, 3 Oct 2018 16:14:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:34416 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726694AbeJCUOV (ORCPT ); Wed, 3 Oct 2018 16:14:21 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id EF226AFB5; Wed, 3 Oct 2018 13:25:54 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 431121E3613; Wed, 3 Oct 2018 15:25:54 +0200 (CEST) Date: Wed, 3 Oct 2018 15:25:54 +0200 From: Jan Kara To: Linus Walleij Cc: Paolo Valente , Johannes Thumshirn , aherrmann@suse.com, Jens Axboe , linux-block , linux-mmc , linux-mtd@lists.infradead.org, Pavel Machek , Ulf Hansson , Richard Weinberger , Artem Bityutskiy , Adrian Hunter , Jan Kara , mgorman@suse.com, Chunyan Zhang , "linux-kernel@vger.kernel.org" , bfq-iosched@googlegroups.com, oleksandr@natalenko.name, Mark Brown Subject: Re: [PATCH] block: BFQ default for single queue devices Message-ID: <20181003132554.GC21043@quack2.suse.cz> References: <20181002124329.21248-1-linus.walleij@linaro.org> <05fdbe23-ec01-895f-e67e-abff85c1ece2@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 03-10-18 08:53:37, Linus Walleij wrote: > On Wed, Oct 3, 2018 at 8:29 AM Paolo Valente wrote: > > > So, I do understand your need for conservativeness, but, after so much > > evidence on single-queue devices, and so many years! :), what's the > > point in keeping Linux worse for virtually everybody, by default? > > I understand if we need to ease things in as well, I don't intend this > change for the current merge window or anything, since v4.19 > will notably have this patch: > > commit d5038a13eca72fb216c07eb717169092e92284f1 > Author: Johannes Thumshirn > Date: Wed Jul 4 10:53:56 2018 +0200 > > scsi: core: switch to scsi-mq by default > > It has been more than one year since we tried to change the default from > legacy to multi queue in SCSI with commit c279bd9e406 ("scsi: default to > scsi-mq"). But due to issues with suspend/resume and performance problems > it had been reverted again with commit cbe7dfa26eee ("Revert "scsi: default > to scsi-mq""). > > In the meantime there have been a substantial amount of performance > improvements and suspend/resume got fixed as well, thus we can re-enable > scsi-mq without a significant performance penalty. > > Signed-off-by: Johannes Thumshirn > Reviewed-by: Hannes Reinecke > Reviewed-by: Ming Lei > Acked-by: John Garry > Signed-off-by: Martin K. Petersen > > I guess that patch can be a bit scary by itself. But IIUC it all went > fine this time! > > But hey, if that works, that means $SUBJECT patch will enable BFQ on all > libata devices and any SCSI that is single queue as well, not just > "obscure" stuff like MMC/SD and UBI, and that is > indeed a massive crowd of legacy devices. But we're talking > v4.21 here. > > Johannes, you might be interested in $SUBJECT patch. > It'd be nice to hear what SUSE people have to add, since they > are pretty proactive in this area. So we do have a udev rules in our distro which sets the IO scheduler based on device parameters (rotational at least, with blk-mq we might start considering number of queues as well, plus we have some exceptions like virtio, loop, etc.). So the kernel default doesn't concern us too much as a distro. I personally would consider bfq a safer default for single-queue devices (loop probably needs exception) but I don't feel too strongly about it. Honza -- Jan Kara SUSE Labs, CR