Messages in this thread | | | Date | Tue, 19 May 2009 10:24:35 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v4] ftrace: add a tracepoint for __raise_softirq_irqoff() |
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* Zhaolei <zhaolei@cn.fujitsu.com> wrote:
> * From: "Xiao Guangrong" <xiaoguangrong@cn.fujitsu.com> > > Steven Rostedt wrote: > >> On Thu, 14 May 2009, Mathieu Desnoyers wrote: > >>>> From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> > >>>> > >>>> 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
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