Messages in this thread | | | From | "Liang, Kan" <> | Subject | RE: [PATCH 1/1] perf/x86/intel/uncore: Add support for Intel SKL client uncore | Date | Thu, 21 Apr 2016 11:55:56 +0000 |
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> > On Wed, 20 Apr 2016, Liang, Kan wrote: > > > On Wed, 20 Apr 2016, Liang, Kan wrote: > > > > > The stop of the box1 events disables the whole machinery on that > > > > > node and therefor the box0 event is wreckaged as well. Hmm? > > > > > > > > > Right. How about check the SKL_UNC_PERF_GLOBAL_CTL in > enable_event? > > > > If it's cleared, we can reset it there. The drawback is that there > > > > will be an extra rdmsrl and a possible wrmsrl. > > > > > > Well, that does not buy anything as you cannot disable the thing at > > > all, unless you have refcounting. And that refcounting needs to be in the > 'type' > > > struct and that would probably be some real pain to implement. > > > > > > The question is whether we need enable/disable at all. If the type > > > is initialized we enable it and on exit we disable it. Ditto on cpu > > > hotplug - which is also used for init to enable all nodes. > > > > > > So if there is no drawback in letting the thing enabled if no events > > > are armed, then we really can do w/o the enable/disable_box callbacks. > > > > > There is no drawback in letting the thing enabled, but PERF_GLOBAL_CTL > > could be disabled after Package C7. I add the enable/disable thing to > > try to workaround it. > > I don't see how that solves it. If a counter is active, then C7 will stop it and > you wont get anything useful from it after returning from C7. Or does an > active counter prevent C7?
Right, the workaround doesn't cover all cases. It helps for the new events and the cases that monitoring a busy system. A busy system means it never enter C7 during the counting. I will mention it in the changelog of V2.
> > > I once did the test on a SKL laptop. If the machine goes idle for a > > while, then the uncore counter will always return 0. For fixing it, we > > have to re-enable PERF_GLOBAL_CTL. > > Hmm, but that does only help for new events after returning from C7, right?
Yes.
> > > I think I made a typo in previous reply. I mean we can check it or > > just force rewrite the PERF_GLOBAL_CTL in enable_box. We don't need > > disable_box since there is no drawback in letting the thing enabled. > > Sure, but then you can just unconditionally enable it. IOW, leave the enable > callback as is.
Will do that in V2.
Thanks, Kan
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