From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH] virtio_blk: merge S/G list entries by default Date: Sun, 7 Sep 2014 20:47:45 +0200 Message-ID: <20140907184745.GA23026@lst.de> References: <1410044994-14943-1-git-send-email-hch@lst.de> <20140907114153.GB26569@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20140907114153.GB26569@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: Jens Axboe , virtualization@lists.linux-foundation.org, Christoph Hellwig , linux-kernel@vger.kernel.org List-Id: virtualization@lists.linuxfoundation.org On Sun, Sep 07, 2014 at 02:41:53PM +0300, Michael S. Tsirkin wrote: > > Signed-off-by: Christoph Hellwig > > OK so this is an optimization patch right? > What kind of performance gain is observed with it? None. I actually wrote it when the block layer had a bug when dm was used on top of the !merge case, and I decided to send it out as there had been no discussion about disabling this by default on the existing blk-mq drivers. At least for my qemu/kvm setup it doesn't make a difference either way, although not doing the cheap merge doesn't like the right kind of optimization to me. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752646AbaIGSru (ORCPT ); Sun, 7 Sep 2014 14:47:50 -0400 Received: from verein.lst.de ([213.95.11.211]:41968 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751354AbaIGSrt (ORCPT ); Sun, 7 Sep 2014 14:47:49 -0400 Date: Sun, 7 Sep 2014 20:47:45 +0200 From: Christoph Hellwig To: "Michael S. Tsirkin" Cc: Christoph Hellwig , Rusty Russell , Jens Axboe , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH] virtio_blk: merge S/G list entries by default Message-ID: <20140907184745.GA23026@lst.de> References: <1410044994-14943-1-git-send-email-hch@lst.de> <20140907114153.GB26569@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140907114153.GB26569@redhat.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Sep 07, 2014 at 02:41:53PM +0300, Michael S. Tsirkin wrote: > > Signed-off-by: Christoph Hellwig > > OK so this is an optimization patch right? > What kind of performance gain is observed with it? None. I actually wrote it when the block layer had a bug when dm was used on top of the !merge case, and I decided to send it out as there had been no discussion about disabling this by default on the existing blk-mq drivers. At least for my qemu/kvm setup it doesn't make a difference either way, although not doing the cheap merge doesn't like the right kind of optimization to me.