From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758115Ab1FVOix (ORCPT ); Wed, 22 Jun 2011 10:38:53 -0400 Received: from merlin.infradead.org ([205.233.59.134]:59208 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753411Ab1FVOiw convert rfc822-to-8bit (ORCPT ); Wed, 22 Jun 2011 10:38:52 -0400 Subject: Re: [RFC][PATCH 1/3] sched, block: Move unplug From: Peter Zijlstra To: Thomas Gleixner Cc: Jens Axboe , "linux-kernel@vger.kernel.org" , Linus Torvalds , Ingo Molnar , Tejun Heo In-Reply-To: References: <20110621233444.094372367@chello.nl> <20110621233648.806475812@chello.nl> <4E019353.6030902@fusionio.com> <4E01F5D6.1020107@fusionio.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Wed, 22 Jun 2011 16:38:01 +0200 Message-ID: <1308753481.1022.27.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2011-06-22 at 16:30 +0200, Thomas Gleixner wrote: > > It is supposedly a real problem, not just an inkling. It's not about > > recursing indefinitely, the plug is fairly bounded. But the IO dispatch > > path can be pretty deep, and if you hit that deep inside the reclaim or > > file system write path, then you get dangerously close. Dave Chinner > > posted some numbers in the 2.6.39-rc1 time frame showing how close we > > got. > > Fair enough. > Ok. So we move it out and keep the from_scheduler flag so that code > does not go down the IO path from there. Won't punting the plug to a worker thread wreck all kinds of io accounting due to the wrong task doing the actual io submission?