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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 7B3C1CA9EC9 for ; Mon, 4 Nov 2019 22:57:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 56CF920663 for ; Mon, 4 Nov 2019 22:57:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729368AbfKDW5j (ORCPT ); Mon, 4 Nov 2019 17:57:39 -0500 Received: from verein.lst.de ([213.95.11.211]:41762 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729122AbfKDW5j (ORCPT ); Mon, 4 Nov 2019 17:57:39 -0500 Received: by verein.lst.de (Postfix, from userid 2407) id 9A4B768BE1; Mon, 4 Nov 2019 23:57:36 +0100 (CET) Date: Mon, 4 Nov 2019 23:57:36 +0100 From: Christoph Hellwig To: Jens Axboe Cc: Keith Busch , Christoph Hellwig , ming.lei@redhat.com, linux-block@vger.kernel.org Subject: Re: [PATCH] block: avoid blk_bio_segment_split for small I/O operations Message-ID: <20191104225736.GA25569@lst.de> References: <20191104180543.23123-1-hch@lst.de> <20191104193002.GA21075@redsun51.ssa.fujisawa.hgst.com> <20191104225036.GA21282@redsun51.ssa.fujisawa.hgst.com> <2822bfe1-5d9d-ec87-9607-36617e528985@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2822bfe1-5d9d-ec87-9607-36617e528985@kernel.dk> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Mon, Nov 04, 2019 at 03:55:41PM -0700, Jens Axboe wrote: > > All existing ones I'm aware of are 128k, so 4k aligned, but if the LBA > > format is 512B, you could start a 4k IO at a 126k offset to straddle the > > boundary. Hm, maybe we don't care about the split penalty in that case > > since unaligned access is already going to be slower for other reasons ... > > Yeah, not sure that's a huge concern for that particular case. If you > think it's a real world issue, it should be possible to set aside a > queue bit for this and always have them hit the slower split path. Well, we use that field for zoned devices also, in which case it is an issue. I think I'll need to send a patch to skip the fast path if we have chunk_sectors set.