From owner-freebsd-current@FreeBSD.ORG Mon Mar 4 15:16:22 2013 Return-Path: Delivered-To: freebsd-current@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id 2B89080E; Mon, 4 Mar 2013 15:16:22 +0000 (UTC) (envelope-from ian@FreeBSD.org) Received: from mho-02-ewr.mailhop.org (mho-04-ewr.mailhop.org [204.13.248.74]) by mx1.freebsd.org (Postfix) with ESMTP id F36A11F99; Mon, 4 Mar 2013 15:16:21 +0000 (UTC) Received: from c-24-8-232-202.hsd1.co.comcast.net ([24.8.232.202] helo=damnhippie.dyndns.org) by mho-02-ewr.mailhop.org with esmtpsa (TLSv1:AES256-SHA:256) (Exim 4.72) (envelope-from ) id 1UCX7l-000Izr-5O; Mon, 04 Mar 2013 15:16:21 +0000 Received: from [172.22.42.240] (revolution.hippie.lan [172.22.42.240]) by damnhippie.dyndns.org (8.14.3/8.14.3) with ESMTP id r24FGHaU091570; Mon, 4 Mar 2013 08:16:17 -0700 (MST) (envelope-from ian@FreeBSD.org) X-Mail-Handler: Dyn Standard SMTP by Dyn X-Originating-IP: 24.8.232.202 X-Report-Abuse-To: abuse@dyndns.com (see http://www.dyndns.com/services/sendlabs/outbound_abuse.html for abuse reporting information) X-MHO-User: U2FsdGVkX1+zywGXsN5SBd4z+krwkjYe Subject: Re: access to hard drives is "blocked" by writes to a flash drive From: Ian Lepore To: Don Lewis In-Reply-To: <201303040301.r2431Rjm008175@gw.catspoiler.org> References: <201303040301.r2431Rjm008175@gw.catspoiler.org> Content-Type: text/plain; charset="us-ascii" Date: Mon, 04 Mar 2013 08:16:17 -0700 Message-ID: <1362410177.1195.234.camel@revolution.hippie.lan> Mime-Version: 1.0 X-Mailer: Evolution 2.32.1 FreeBSD GNOME Team Port Content-Transfer-Encoding: 7bit Cc: deeptech71@gmail.com, phk@phk.freebsd.dk, freebsd-current@FreeBSD.org, peter@rulingia.com X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 04 Mar 2013 15:16:22 -0000 On Sun, 2013-03-03 at 19:01 -0800, Don Lewis wrote: > On 3 Mar, Poul-Henning Kamp wrote: > > > For various reasons (see: Lemming-syncer) FreeBSD will block all I/O > > traffic to other disks too, when these pileups gets too bad. > > The Lemming-syncer problem should have mostly been fixed by 231160 in > head (231952 in stable/9 and 231967 in stable/8) a little over a year > ago. The exceptions are atime updates, mmaped files with dirty pages, > and quotas. Under certain workloads I still notice periodic bursts of > seek noise. After thinking about it for a bit, I suspect that it could > be atime updates, but I haven't tried to confirm that. > > When using TCQ or NCQ, perhaps we should limit the number of outstanding > writes per device to leave some slots open for reads. We should > probably also prioritize reads over writes unless we are under memory > pressure. > Then either those changes didn't have the intended effect, or the problem we're seeing with lack of system responsiveness when there's a large backlog of writes to a slow device is not the lemming-syncer problem. It's also not a lack of TCQ/NCQ slots, given that no such thing exists with SD card IO. When this is going on, the process driving the massive output spends almost all its time in a wdrain wait, and if you try to launch an app that isn't already in cache, a siginfo generally shows it to be in a getblk wait. -- Ian