Messages in this thread | | | Subject | Re: [PATCH] perf_events: improve x86 event scheduling (v5) | From | Peter Zijlstra <> | Date | Tue, 19 Jan 2010 17:25:23 +0100 |
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On Tue, 2010-01-19 at 16:55 +0100, Frederic Weisbecker wrote: > > Also, I see you set an ->unthrottle, but then don't implement it, but > > comment it as todo, which is strange because that implies its broken. If > > there's an ->unthrottle method it will throttle, so if its todo, the > > safest thing is to not set it. > > > Yeah, that's because I have a too vague idea on what is the purpose > of the unthrottle() callback. > > I've read the concerned codes that call this, several times, and I still > can't figure out what happens there, not sure what is meant by throttle > or unthrottle there :-/
OK, so not setting it is relatively safe.
As to what it does, it has to undo everything you do when perf_event_overflow() returns true, which happens when ->unthrottle is set and we get more than sysctl_perf_event_sample_rate/HZ events in a jiffy.
If you look at the x86 implementation, you'll see that we simply disable the hardware counter when the overflow call returns true, so the unthrottle() callback simply enables it again.
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