Re: [PATCH 4/4] [x86] perf: fix accidentally ack'ing a second event on intel perf counter

Don Zickus
2010-09-03T14:03:52Z

On Fri, Sep 03, 2010 at 01:02:49PM +0200, Stephane Eranian wrote:
> Here is an example of what I gathered on a Westmere:
>
> This is coming into the interrupt handler:
> - status = overflow status coming from GLOBAL_OVF_STATUS
> - status2 = inspection of the counters
> - act = cpuc->active_mask[0]
>
> In case both status don't match, I dump the state of the active events
> incl. the counter values(val).
>
> [ 822.813808] CPU2 irqin status=0x6 status2=0x4 act=0x7
> [ 822.813818] CPU2 cfg=0x13003c idx=0 sel=53003c val=ffffa833f298
> [ 822.813821] CPU2 cfg=0x12003c idx=1 sel=52003c val=fffffe130229
> [ 822.813823] CPU2 cfg=0x11003c idx=2 sel=51003c val=5e9
>
> Here only counter2 has overflowed, yet the handler will also process counter1
> which is wrong.

Hmm, the test case I used was 'perf top'. This was only using perf
counter0. So I am not sure, at least in my case, it was a stale event.
Though I don't think I remember checking the status immediately after
acking it just to verify the ack worked.

I'll poke some more on my machine today.

Cheers,
Don