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=-7.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D067CC6369E for ; Thu, 3 Dec 2020 03:26:45 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0DD1720643 for ; Thu, 3 Dec 2020 03:26:44 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0DD1720643 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=tempfail smtp.mailfrom=dm-devel-bounces@redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606966001; h=from:from:sender:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:list-id:list-help: list-unsubscribe:list-subscribe:list-post; bh=YCC22kA9BfS7d5D34gfcTwvkVFsR3+F2aB48/+c/SFU=; b=ZJFK0m43YvvJdJAvuKMsvBDn2UAMOgPxwLDz7cq8xvdZdkyPYCSAbYqREa3PCpkXfDxFEs x6UPL4J4w0TsaEXBLqLm9SFcd9GyzC+wj5oxOrVjk02THxFWCAOi80zdbPsO14nmCjmJM1 gXOWmnvJDOuZNVhZL+VGQdCUU7EsdNs= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-511-gZ8eS6vFOGS64ygwKKpjpQ-1; Wed, 02 Dec 2020 22:26:39 -0500 X-MC-Unique: gZ8eS6vFOGS64ygwKKpjpQ-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E41EE1007B05; Thu, 3 Dec 2020 03:26:33 +0000 (UTC) Received: from colo-mx.corp.redhat.com (colo-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.20]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0CBD019C46; Thu, 3 Dec 2020 03:26:33 +0000 (UTC) Received: from lists01.pubmisc.prod.ext.phx2.redhat.com (lists01.pubmisc.prod.ext.phx2.redhat.com [10.5.19.33]) by colo-mx.corp.redhat.com (Postfix) with ESMTP id 452A5180954D; Thu, 3 Dec 2020 03:26:31 +0000 (UTC) Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) by lists01.pubmisc.prod.ext.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id 0B33QTlR011578 for ; Wed, 2 Dec 2020 22:26:29 -0500 Received: by smtp.corp.redhat.com (Postfix) id 3609C5C1BD; Thu, 3 Dec 2020 03:26:29 +0000 (UTC) Received: from T590 (ovpn-12-87.pek2.redhat.com [10.72.12.87]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8BD8C5C1B4; Thu, 3 Dec 2020 03:26:13 +0000 (UTC) Date: Thu, 3 Dec 2020 11:26:08 +0800 From: Ming Lei To: Mike Snitzer Message-ID: <20201203032608.GD540033@T590> References: <20201130171805.77712-1-snitzer@redhat.com> <20201201160709.31748-1-snitzer@redhat.com> MIME-Version: 1.0 In-Reply-To: <20201201160709.31748-1-snitzer@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-loop: dm-devel@redhat.com Cc: axboe@kernel.dk, martin.petersen@oracle.com, jdorminy@redhat.com, bjohnsto@redhat.com, linux-block@vger.kernel.org, dm-devel@redhat.com Subject: Re: [dm-devel] [PATCH v2] block: use gcd() to fix chunk_sectors limit stacking X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Tue, Dec 01, 2020 at 11:07:09AM -0500, Mike Snitzer wrote: > commit 22ada802ede8 ("block: use lcm_not_zero() when stacking > chunk_sectors") broke chunk_sectors limit stacking. chunk_sectors must > reflect the most limited of all devices in the IO stack. > > Otherwise malformed IO may result. E.g.: prior to this fix, > ->chunk_sectors = lcm_not_zero(8, 128) would result in > blk_max_size_offset() splitting IO at 128 sectors rather than the > required more restrictive 8 sectors. What is the user-visible result of splitting IO at 128 sectors? I understand it isn't related with correctness, because the underlying queue can split by its own chunk_sectors limit further. So is the issue too many further-splitting on queue with chunk_sectors 8? then CPU utilization is increased? Or other issue? > > And since commit 07d098e6bbad ("block: allow 'chunk_sectors' to be > non-power-of-2") care must be taken to properly stack chunk_sectors to > be compatible with the possibility that a non-power-of-2 chunk_sectors > may be stacked. This is why gcd() is used instead of reverting back > to using min_not_zero(). I guess gcd() won't be better because gcd(a,b) is <= max(a, b), so bio size is decreased much with gcd(a, b), and IO performance should be affected. Maybe worse than min_not_zero(a, b) which is often > gcd(a, b). Thanks, Ming -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel