RE: [PATCH 1/1] perf/x86/intel/uncore: Add support for Intel SKL client uncore

[Liang, Kan]

> 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 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.
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.
The HSW and BDW client also have similar errata. If it's OK for you, I will send
another patch for them.

Thanks,
Kan