Messages in this thread | | | Subject | Re: [PATCH 2/2] perf_counter: optimize context switch between identical inherited contexts | From | Peter Zijlstra <> | Date | Fri, 22 May 2009 12:08:17 +0200 |
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On Fri, 2009-05-22 at 19:56 +1000, Paul Mackerras wrote: > Peter Zijlstra writes: > > > On Fri, 2009-05-22 at 14:27 +1000, Paul Mackerras wrote: > > > Since we don't have individual fds for the counters in a cloned > > > context, the only thing that can make two clones of a given parent > > > different after they have been cloned is enabling or disabling all > > > counters with prctl. To account for this, we keep a count of the > > > number of enabled counters in each context. Two contexts must have > > > the same number of enabled counters to be considered equivalent. > > > > Curious point that.. so prctl() can disable counters it doesn't own. > > > > Shouldn't we instead fix that? > > Well, prctl enables/disables the counters that are counting on the > current process, regardless of who or what created them. I always > thought that was a little strange; maybe it is useful to be able to > disable all the counters that any other process might have put on to > you, but I can't think of a scenario where you'd really need to do > that, particularly since the disable is a one-shot operation, and > doesn't prevent new (enabled) counters being attached to you. > > On the other hand, what does "all the counters I own" mean? Does it > mean all the ones that I have fds open for? Or does it mean all the > ones that I created? Either way we don't have a good way to enumerate > them.
I'm for all counters you created (ie have a fd for). Being able to disable counters others created on you just sounds wrong.
If we can settle on a semantic, I'm sure we can implement it :-)
Ingo, Corey, any opinions?
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