Messages in this thread | | | Date | Thu, 18 Dec 2008 12:16:12 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH v2] tracing/function-graph-tracer: prevent from hrtimer interrupt infinite loop |
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* Frédéric Weisbecker <fweisbec@gmail.com> wrote:
> 2008/12/18 Ingo Molnar <mingo@elte.hu>: > > > > * Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > >> Impact: fix a system hang on slow systems > >> > >> While testing the function graph tracer on VirtualBox, I had a system hang > >> immediatly after enabling the tracer. > >> > >> If hrtimer is enabled on kernel, a slow system can spend too much time > >> during tracing the hrtimer_interrupt which will do eternal loops, > >> assuming it always have to retry its process because too much time > >> elapsed during its time update. Now we provide a feature which lurks at > >> the number of retries on hrtimer_interrupt. After 10 retries, the > >> function graph tracer will definetly stop its tracing. > > > > hm, i dont really like this solution - it just works around the problem by > > 'speeding up' the system. If we have a _real_ slow system, there's no such > > way for us to speed it up. > > > It doesn' speed up the system actually. That's not the goal of this > patch.
i meant that abstractly. The "solution" here is that your patch turns off the function-graph-tracer. The practical effect of that is: the system gets much faster at processing hrtimer IRQs and effectively "speeds up".
ok?
Ingo -- 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/
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