From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754451AbZBBInA (ORCPT ); Mon, 2 Feb 2009 03:43:00 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752362AbZBBImw (ORCPT ); Mon, 2 Feb 2009 03:42:52 -0500 Received: from hp3.statik.tu-cottbus.de ([141.43.120.68]:56713 "EHLO hp3.statik.tu-cottbus.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752294AbZBBImv (ORCPT ); Mon, 2 Feb 2009 03:42:51 -0500 Message-ID: <4986B205.2040807@s5r6.in-berlin.de> Date: Mon, 02 Feb 2009 09:42:45 +0100 From: Stefan Richter User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.8.1.19) Gecko/20081204 SeaMonkey/1.1.14 MIME-Version: 1.0 To: Benjamin Herrenschmidt CC: Frederic Weisbecker , Arjan van de Ven , Ingo Molnar , linux-kernel@vger.kernel.org, Andrew Morton , Lai Jiangshan , Peter Zijlstra , Steven Rostedt Subject: Re: [RFC][PATCH] create workqueue threads only when needed References: <20090127001708.GA4815@nowhere> <20090126163015.7f879b18@infradead.org> <20090131180347.GC5884@nowhere> <20090131101502.7ce8e7af@infradead.org> <20090131182843.GD5884@nowhere> <1233524261.18767.60.camel@pasglop> <20090202022414.GA5006@nowhere> <1233554443.18767.71.camel@pasglop> In-Reply-To: <1233554443.18767.71.camel@pasglop> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Benjamin Herrenschmidt wrote: > On Mon, 2009-02-02 at 03:24 +0100, Frederic Weisbecker wrote: >> On Mon, Feb 02, 2009 at 08:37:41AM +1100, Benjamin Herrenschmidt wrote: >> > >> > > I don't know, most of those I've looked on are not documented about the reason >> > > for a private workqueue. I guess most of them can use the usual kevent. I rather suspect that the majority of private workqueues are there for good reasons. >> > The main problem with kevent is that it gets clogged up. >> >> I don't think so. Here is a snapshot of the workqueue tracer in my >> box currently: > > That's not quite what I meant ... > > The main problem with keventd I'd say is that it's used in all sort of > exeptional code path (ie, driver reset path, error handling, etc...) for > things that will msleep happily for tenth milliseconds, that sort of > thing. > > IE. It will be pretty responsive -in general- but can suffer form > horrible latencies every now and then. Actually it /should/ be the other way around: The shared workqueue should only be used for work that sleeps only briefly (perhaps with the exception of very unlikely longer sleeps e.g. for allocations that cause paging). Work which /may/ sleep longer, for example performs SCSI transactions, needs to go into a private workqueue or other kind of context. OTOH you are right too; work which must not be deferred too long by work from another uncooperative/ unfair subsystem is probably also better off in an own workqueue... -- Stefan Richter -=====-==--= --=- ---=- http://arcgraph.de/sr/