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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 12CE1C433E0 for ; Thu, 25 Feb 2021 20:48:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BBE9A60201 for ; Thu, 25 Feb 2021 20:48:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232761AbhBYUsj (ORCPT ); Thu, 25 Feb 2021 15:48:39 -0500 Received: from mail110.syd.optusnet.com.au ([211.29.132.97]:41483 "EHLO mail110.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229993AbhBYUsi (ORCPT ); Thu, 25 Feb 2021 15:48:38 -0500 Received: from dread.disaster.area (pa49-179-130-210.pa.nsw.optusnet.com.au [49.179.130.210]) by mail110.syd.optusnet.com.au (Postfix) with ESMTPS id 52BA2104CD9; Fri, 26 Feb 2021 07:47:56 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1lFNYB-004Ewj-LN; Fri, 26 Feb 2021 07:47:55 +1100 Date: Fri, 26 Feb 2021 07:47:55 +1100 From: Dave Chinner To: Christoph Hellwig Cc: "Darrick J. Wong" , linux-xfs@vger.kernel.org Subject: Re: [PATCH 2/8] xfs: separate CIL commit record IO Message-ID: <20210225204755.GK4662@dread.disaster.area> References: <20210223033442.3267258-1-david@fromorbit.com> <20210223033442.3267258-3-david@fromorbit.com> <20210224203429.GR7272@magnolia> <20210224214417.GB4662@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=Tu+Yewfh c=1 sm=1 tr=0 cx=a_idp_d a=JD06eNgDs9tuHP7JIKoLzw==:117 a=JD06eNgDs9tuHP7JIKoLzw==:17 a=kj9zAlcOel0A:10 a=qa6Q16uM49sA:10 a=VwQbUJbxAAAA:8 a=7-415B0cAAAA:8 a=ABxO-cM9r7JnYSn4Z-wA:9 a=CjuIK1q_8ugA:10 a=AjGcO6oz07-iQ99wixmX:22 a=biEYGPWJfzWAr4FL6Ov7:22 Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Thu, Feb 25, 2021 at 09:34:47AM +0100, Christoph Hellwig wrote: > On Thu, Feb 25, 2021 at 08:44:17AM +1100, Dave Chinner wrote: > > > Also, do you have any idea what was Christoph talking about wrt devices > > > with no-op flushes the last time this patch was posted? This change > > > seems straightforward to me (assuming the answers to my two question are > > > 'yes') but I didn't grok what subtlety he was alluding to...? > > > > He was wondering what devices benefited from this. It has no impact > > on highspeed devices that do not require flushes/FUA (e.g. high end > > intel optane SSDs) but those are not the devices this change is > > aimed at. There are no regressions on these high end devices, > > either, so they are largely irrelevant to the patch and what it > > targets... > > I don't think it is that simple. Pretty much every device aimed at > enterprise use does not enable a volatile write cache by default. That > also includes hard drives, arrays and NAND based SSDs. > > Especially for hard drives (or slower arrays) the actual I/O wait might > matter. Sorry, I/O wait might matter for what? I'm really not sure what you're objecting to - you've hand-waved about hardware that doesn't need cache flushes twice now and inferred that they'd be adversely affected by removing cache flushes. That just doesn't make any sense at all, and I have numbers to back it up. You also asked what storage it improved performance on and I told you and then also pointed out all the software layers that it massively helps, too, regardless of the physical storage characteristics. https://lore.kernel.org/linux-xfs/20210203212013.GV4662@dread.disaster.area/ I have numbers to back it up. You did not reply to me, so I'm not going to waste time repeating myself here. > What is the argument against making this conditional? There is no argument for making this conditional. You've created an undefined strawman and are demanding that I prove it wrong. If you've got anything concrete, then tell us about it directly and provide numbers. Cheers, Dave. -- Dave Chinner david@fromorbit.com