From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757386AbZGCJpU (ORCPT ); Fri, 3 Jul 2009 05:45:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755706AbZGCJpI (ORCPT ); Fri, 3 Jul 2009 05:45:08 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:54771 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753176AbZGCJpG (ORCPT ); Fri, 3 Jul 2009 05:45:06 -0400 Date: Fri, 3 Jul 2009 11:44:50 +0200 From: Ingo Molnar To: Lai Jiangshan Cc: Zhaolei , Thomas Gleixner , Peter Zijlstra , Mathieu Desnoyers , Steven Rostedt , linux-kernel@vger.kernel.org, fweisbec@gmail.com, Li Zefan , Xiao Guangrong Subject: Re: [PATCH v4] ftrace: add a tracepoint for __raise_softirq_irqoff() Message-ID: <20090703094450.GB21141@elte.hu> References: <20090511151353.GA14391@Krystal> <4A094677.5090900@cn.fujitsu.com> <4A0BF82A.2070208@cn.fujitsu.com> <20090514124013.GC21241@Krystal> <4A0CCB2E.10202@cn.fujitsu.com> <6A70E08D65F749FA92475F8BA1F9510D@zhaoleiwin> <20090519082435.GB15286@elte.hu> <4A4DD0C7.6070401@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A4DD0C7.6070401@cn.fujitsu.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Lai Jiangshan wrote: > Ingo Molnar wrote: > > * Zhaolei wrote: > > > >> * From: "Xiao Guangrong" > >>> Steven Rostedt wrote: > >>>> On Thu, 14 May 2009, Mathieu Desnoyers wrote: > >>>>>> From: Mathieu Desnoyers > >>>>>> > >>>>>> This patch is modified from Mathieu Desnoyers' patch. The original patch > >>>>>> can be found here: > >>>>>> http://marc.info/?l=linux-kernel&m=123791201816245&w=2 > >>>>>> This tracepoint can trace the time stamp when softirq action is raised. > >>>>>> > >>>>>> Changelog for v1 -> v2: > >>>>>> 1: Use TRACE_EVENT instead of DEFINE_TRACE > >>>>>> 2: Move the tracepoint from raise_softirq_irqoff() to > >>>>>> __raise_softirq_irqoff() > >>>>>> > >>>>>> Changelog for v2 -> v3: > >>>>>> Move the definition of __raise_softifq_irqoff() to .c file when > >>>>>> CONFIG_TRACEPOINTS is enabled, to avoid recursive includes > >>>>>> > >>>>>> Changelog for v3 -> v4: > >>>>>> 1: Come back to v2, and use forward declarations to avoid > >>>>>> recursive includes as Mathieu's suggestion > >>>>>> 2: Modifiy the tracepoint name > >>>>>> 3: Add comments for this tracepoint > >>>>>> > >>>>> This is a step in the right direction, but please see my email to Lai > >>>>> about the fact that this assumes correct and undocumented include > >>>>> dependencies in kernel/trace/events.c. Not explicitely stating the > >>>>> include dependencies is a build error waiting to happen. > >>>>> > >>>>> Including interrupt.h under a ifdef would allow keeping track of > >>>>> TRACE_EVENT specific build dependencies neatly on a per header basis. > >>>> This is all moot, the events.c file no longer exists and as not an issue. > >>>> > >>> As Steve's says, use ftrace in ftrace.h not in events.c now. > >>> So, this mistake does not exist. > >>> Dose this patch has other error? I expect for your views. > >>> > >>> Thanks for your review, is great help to me. ;-) > >> Hello, > >> > >> It seems Mathieu has no other comments on this patch now. > >> Ingo, what is your opinion on this patch? > > > > There's a complication: this area of the softirq code needs fixes > > (unrelated to tracing). > > > > This API: > > > > inline void raise_softirq_irqoff(unsigned int nr) > > { > > __raise_softirq_irqoff(nr); > > > > /* > > * If we're in an interrupt or softirq, we're done > > * (this also catches softirq-disabled code). We will > > * actually run the softirq once we return from > > * the irq or softirq. > > * > > * Otherwise we wake up ksoftirqd to make sure we > > * schedule the softirq soon. > > */ > > if (!in_interrupt()) > > wakeup_softirqd(); > > } > > > > is broken with RT tasks (as recently reported to lkml), as when a > > real-time task wakes up ksoftirqd (which has lower priority) it wont > > execute and we starve softirq execution. > > > > The proper solution would be to have a new API: > > > > raise_softirq_check() > > > > and to remove the wakeup_softirqd() hack from raise_softirq_irqoff() > > - and put raise_softirq_check() to all places that use > > raise_softirq*() from process context. > > > > raise_softirq_check() would execute softirq handlers from process > > context, if there's any pending ones. It has to be called outside of > > bh critical sections - i.e. often a bit after the raise_softirq() > > has been done. > > > > __raise_softirq_irqoff() would be made private to kernel/softirq.c, > > and we'd only have two public APIs to trigger softirqs: > > raise_softirq() and raise_softirq_irqoff(). Both just set the > > pending flag and dont do any wakeup. > > > > As a side-effect of these fixes, the tracepoints will be sorted out > > as well - there wont be any need to hack into > > __raise_softirq_irqoff(). > > > > Ingo > > > > Hi, Ingo > > Could you give me the .config file that this bug occurs? I havent reproduced this - it was reported in a recent thread on lkml. I dont have an URI for it - does anyone on the Cc: remember the details? Ingo