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=-8.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 85CB6C43461 for ; Thu, 10 Sep 2020 21:21:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 35EDB221E5 for ; Thu, 10 Sep 2020 21:21:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CtFaCt5W" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725965AbgIJVVO (ORCPT ); Thu, 10 Sep 2020 17:21:14 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:33030 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731126AbgIJOZr (ORCPT ); Thu, 10 Sep 2020 10:25:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1599747885; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=W2uRnQnP1ed2gvxzbsFcdmIP/DbyExQBxh8KjxEaNic=; b=CtFaCt5WXmS0QgE3CzBgcje4dUC3509oM7+1QAr5q0hKlAq/JwVyECUXRKKD+TrOsoobgV sSRs4AQCyT6pvbhWiKhPkJOgKvIYARYxWRSOpkXh/cydSNHQF14ny9s7KC8I7/pjGhRC8q dx5fYZwnIWSJSrocKa/QGuEN2Optzko= 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-263-YRVyuaNbMAaD2OIllsioxA-1; Thu, 10 Sep 2020 10:24:44 -0400 X-MC-Unique: YRVyuaNbMAaD2OIllsioxA-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 106CF80EF8C; Thu, 10 Sep 2020 14:24:43 +0000 (UTC) Received: from localhost (unknown [10.18.25.174]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BFD6D27BDD; Thu, 10 Sep 2020 14:24:39 +0000 (UTC) Date: Thu, 10 Sep 2020 10:24:39 -0400 From: Mike Snitzer To: Vijayendra Suman Cc: dm-devel@redhat.com, linux-block@vger.kernel.org Subject: Re: Revert "dm: always call blk_queue_split() in dm_process_bio()" Message-ID: <20200910142438.GA21919@redhat.com> References: <529c2394-1b58-b9d8-d462-1f3de1b78ac8@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <529c2394-1b58-b9d8-d462-1f3de1b78ac8@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org [cc'ing dm-devel and linux-block because this is upstream concern too] On Wed, Sep 09 2020 at 1:00pm -0400, Vijayendra Suman wrote: > Hello Mike, > > While Running pgbench tool with 5.4.17 kernel build > > Following performance degrade is found out > > buffer read/write metric : -17.2% > cache read/write metric : -18.7% > disk read/write metric : -19% > > buffer > number of transactions actually processed: 840972 > latency average = 24.013 ms > tps = 4664.153934 (including connections establishing) > tps = 4664.421492 (excluding connections establishing) > > cache > number of transactions actually processed: 551345 > latency average = 36.949 ms > tps = 3031.223905 (including connections establishing) > tps = 3031.402581 (excluding connections establishing) > > After revert of Commit > 2892100bc85ae446088cebe0c00ba9b194c0ac9d ( Revert "dm: always call > blk_queue_split() in dm_process_bio()") I assume 2892100bc85ae446088cebe0c00ba9b194c0ac9d is 5.4-stable's backport of upstream commit 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74 ? > Performance is Counter measurement > > buffer -> > number of transactions actually processed: 1135735 > latency average = 17.799 ms > tps = 6292.586749 (including connections establishing) > tps = 6292.875089 (excluding connections establishing) > > cache -> > number of transactions actually processed: 648177 > latency average = 31.217 ms > tps = 3587.755975 (including connections establishing) > tps = 3587.966359 (excluding connections establishing) > > Following is your commit > > diff --git a/drivers/md/dm.c b/drivers/md/dm.c > index cf71a2277d60..1e6e0c970e19 100644 > --- a/drivers/md/dm.c > +++ b/drivers/md/dm.c > @@ -1760,8 +1760,9 @@ static blk_qc_t dm_process_bio(struct mapped_device > *md, > * won't be imposed. > */ > if (current->bio_list) { > - blk_queue_split(md->queue, &bio); > - if (!is_abnormal_io(bio)) > + if (is_abnormal_io(bio)) > + blk_queue_split(md->queue, &bio); > + else > dm_queue_split(md, ti, &bio); > } > > Could you have a look if it is safe to revert this commit. No, it really isn't a good idea given what was documented in the commit header for commit 120c9257f5f19e5d1e87efcbb5531b7cd81b7d74 -- the excessive splitting is not conducive to performance either. So I think we need to identify _why_ reverting this commit is causing such a performance improvement. Why is calling blk_queue_split() before dm_queue_split() benefiting your pgbench workload? Thanks, Mike