From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f174.google.com ([209.85.216.174]:53626 "EHLO mail-qt0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751654AbdJFSgi (ORCPT ); Fri, 6 Oct 2017 14:36:38 -0400 Received: by mail-qt0-f174.google.com with SMTP id n61so5131279qte.10 for ; Fri, 06 Oct 2017 11:36:37 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <33e52793-251d-ed58-fb59-5432946efb56@coly.li> References: <1506497553-12552-1-git-send-email-tang.junhui@zte.com.cn> <2c39cd9c-34bd-5982-9fd7-ceb61305c13d@coly.li> <6a2052da-6b52-9c06-b85e-e3ea29e3f8e8@coly.li> <18f2271b-87c2-530d-12da-dc2b4a5af1fd@coly.li> <33e52793-251d-ed58-fb59-5432946efb56@coly.li> From: Michael Lyle Date: Fri, 6 Oct 2017 11:36:36 -0700 Message-ID: Subject: Re: [PATCH 4/5] bcache: writeback: collapse contiguous IO better To: Coly Li Cc: Hannes Reinecke , Junhui Tang , linux-bcache@vger.kernel.org, linux-block@vger.kernel.org, Kent Overstreet Content-Type: text/plain; charset="UTF-8" Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org Sorry I missed this question: > Is it the time from writeback starts to dirty reaches dirty target, or > the time from writeback starts to dirty reaches 0 ? Not quite either. I monitor the machine with zabbix; it's the time to when the backing disk reaches its background rate of activity / when writeback hits its minimum rate (writeback with the PI controller writes a little past the target because of the integral term). Viewed one way: 5/80 is just a few percent of difference (6%). But: I'm hopeful that further improvement can be made along this patch series, and in any event it's 5 minutes earlier that I/O will have an unencumbered response time after a pulse of load. Mike