Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751395AbWHIWGF (ORCPT ); Wed, 9 Aug 2006 18:06:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751396AbWHIWGF (ORCPT ); Wed, 9 Aug 2006 18:06:05 -0400 Received: from mx02.stofanet.dk ([212.10.10.12]:11984 "EHLO mx02.stofanet.dk") by vger.kernel.org with ESMTP id S1751395AbWHIWGD (ORCPT ); Wed, 9 Aug 2006 18:06:03 -0400 Date: Thu, 10 Aug 2006 00:05:57 +0200 (CEST) From: Esben Nielsen X-X-Sender: simlo@frodo.shire To: Bill Huey cc: Steven Rostedt , Robert Crocombe , linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner , Darren Hart Subject: Re: [Patch] restore the RCU callback to defer put_task_struct() Re: Problems with 2.6.17-rt8 In-Reply-To: <20060808030524.GA20530@gnuppy.monkey.org> Message-ID: References: <1154541079.25723.8.camel@localhost.localdomain> <1154615261.32264.6.camel@localhost.localdomain> <20060808025615.GA20364@gnuppy.monkey.org> <20060808030524.GA20530@gnuppy.monkey.org> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1945 Lines: 54 On Mon, 7 Aug 2006, Bill Huey wrote: > On Mon, Aug 07, 2006 at 07:56:15PM -0700, Bill Huey wrote: >> On Thu, Aug 03, 2006 at 10:27:41AM -0400, Steven Rostedt wrote: >> >> ...(output and commentary a log deleted)... >> >>> This could also have a side effect that messes things up. >>> >>> Unfortunately, right now I'm assigned to other tasks and I cant spend >>> much more time on this at the moment. So hopefully, Ingo, Thomas or >>> Bill, or someone else can help you find the reason for this problem. >> >> Steve and company, >> >> Speaking of which, after talking to Steve about this and confirming this >> with a revert of changes. put_task_struct() can't deallocated memory from >> either the zone or SLAB cache without taking a sleeping lock. It can't >> be called directly from finish_task_switch to reap the thread because of >> that (violation in atomic). >> >> It is for this reason the RCU call back to delay processing was put into >> place to reap threads and was, seemingly by accident, missing from >> patch-2.6.17-rt7 to -rt8. That is what broke it in the first place. >> >> I tested it with a "make -j4" which triggers the warning and it they all >> go away now. >> >> Reverse patch attached: > > Resend with instrumentation code removed: > > bill > > I had a long discussion with Paul McKenney about this. I opposed the patch from a latency point of view: Suddenly a high-priority RT task could be made into releasing a task_struct. It would be better for latencies to defer it to a low priority task. The conclusion we ended up with was that it is not a job for the RCU system, but it ought to be deferred to some other low priority task to free the task_struct. Esben - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/