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Re: [PATCH tracing/kprobes] kprobes: Disable booster when CONFIG_PREEMPT=y
- From: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- To: Masami Hiramatsu <mhiramat at redhat dot com>
- Cc: Ingo Molnar <mingo at elte dot hu>, Thomas Gleixner <tglx at linutronix dot de>, Peter Zijlstra <a dot p dot zijlstra at chello dot nl>, "Fr??d??ric Weisbecker" <fweisbec at gmail dot com>, Steven Rostedt <rostedt at goodmis dot org>, lkml <linux-kernel at vger dot kernel dot org>, systemtap <systemtap at sources dot redhat dot com>, DLE <dle-develop at lists dot sourceforge dot net>, Ananth N Mavinakayanahalli <ananth at in dot ibm dot com>, Jim Keniston <jkenisto at us dot ibm dot com>
- Date: Fri, 29 Jan 2010 12:08:17 -0500
- Subject: Re: [PATCH tracing/kprobes] kprobes: Disable booster when CONFIG_PREEMPT=y
- References: <4B5E476C.9030303@redhat.com> <20100127215531.24775.26807.stgit@dhcp-100-2-132.bos.redhat.com> <20100129092135.GE10878@elte.hu> <4B62F61D.5060203@redhat.com>
* Masami Hiramatsu (mhiramat@redhat.com) wrote:
> Ingo Molnar wrote:
> >
> > * Masami Hiramatsu <mhiramat@redhat.com> wrote:
> >
> >> Disable kprobe booster when CONFIG_PREEMPT=y, because it can't ensure that
> >> all kernel threads preempted on kprobe's boosted slot run out from the slot
> >> even using freeze_processes().
> >
> > hm, this really sucks as it makes preemptible kernels perform worse. Is there
> > no better solution?
> >
> >> The booster on preemptive kernel will be resumed if synchronize_tasks() or
> >> something like that is introduced.
> >
> > such as this one?
>
> Yes, I think this synchronize_tasks(), which just (sleeping) wait until
> all currently preempted tasks are wake up and scheduled, can ensure safety
If a task is set as stopped, and the preempted before calling schedule,
can this result in a preempted task staying in that state for an
arbitrary long period of time ? Or is there some mechanism prohibiting
that in the scheduler ?
Thanks,
Mathieu
>
> Thank you,
>
> --
> Masami Hiramatsu
>
> Software Engineer
> Hitachi Computer Products (America), Inc.
> Software Solutions Division
>
> e-mail: mhiramat@redhat.com
>
--
Mathieu Desnoyers
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