From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751647AbbD3RAF (ORCPT ); Thu, 30 Apr 2015 13:00:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42958 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750710AbbD3RAB (ORCPT ); Thu, 30 Apr 2015 13:00:01 -0400 From: Jeff Moyer To: Ming Lei Cc: Jens Axboe , Linux Kernel Mailing List , "Justin M. Forbes" , "v4.0" Subject: Re: [PATCH] block: loop: avoiding too many pending per work I/O References: <1430235461-8862-1-git-send-email-ming.lei@canonical.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Thu, 30 Apr 2015 12:59:59 -0400 In-Reply-To: (Ming Lei's message of "Wed, 29 Apr 2015 12:57:27 +0800") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ming Lei writes: > On Wed, Apr 29, 2015 at 12:36 AM, Jeff Moyer wrote: >> Ming Lei writes: >> >>> If there are too many pending per work I/O, too many >>> high priority work thread can be generated so that >>> system performance can be effected. >>> >>> This patch limits the max pending per work I/O as 16, >>> and will fackback to single queue mode when the max >>> number is reached. >> >> Actually, it limits it to 32. Also, there is no discussion on what >> variables might affect this number. Will that magic number change >> depending on the number of cpus on the system, for example? > > My fault, it should have been 16. > > It is just used to keep more IOs in flight, but can't cause obvious > costs like the case of Fedora live booting. > > IMO, it shouldn't depend much on number of CPUs, and more > related with I/O performance of the backing file, and the number > is like 'iodepth' of fio. OK, that makes more sense. I'm still not a huge fan of hard-coding numbers that are storage-specific, but I don't have a better suggestion at the moment, either. Cheers, Jeff