From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759480Ab1IKCvg (ORCPT ); Sat, 10 Sep 2011 22:51:36 -0400 Received: from mail-gw0-f42.google.com ([74.125.83.42]:52785 "EHLO mail-gw0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751514Ab1IKCvf (ORCPT ); Sat, 10 Sep 2011 22:51:35 -0400 Date: Sun, 11 Sep 2011 11:51:28 +0900 From: Tejun Heo To: Shaohua Li Cc: lkml , Jens Axboe , Vivek Goyal Subject: Re: [RFC]block: don't mark flush request as SOFTBARRIER Message-ID: <20110911025128.GM29319@htj.dyndns.org> References: <1315445394.29510.71.camel@sli10-conroe> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1315445394.29510.71.camel@sli10-conroe> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Sep 08, 2011 at 09:29:54AM +0800, Shaohua Li wrote: > I'm wondering why flush request should be marked as > SOFTBARRIER. Current flush sequence guarantees the correctness of > flush even the request is reordered by ioscheduler. The primary reason would be because when those flush data requests are put on the dispatch queue, it doesn't go through elv_dispatch_sort(). SOFTBARRIERs function as dispatch sort boundaries and queueing flush data request at the head w/o SOFTBARRIER would confuse dispatch sorting, and we want to put it at the head of dispatch queue to decrease latency for flush sequence. Thanks. -- tejun