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SubjectRe: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units
On Tue, Jan 07, 2014 at 01:52:31AM +0100, Andi Kleen wrote:
> > > Also of course it requires disabling/enabling PT explicitly for
> > > every perf message, which is slow. So you add at least 2*WRMSR cost
> > > (thousands of cycles).
> >
> > That's just dumb, no flush the entire PT buffer into a few large
> > records.
>
> How would that work?
>
> You mean a separate buffer and then copy or map?
>
> ------
>
> Also here are some more problems with interleaving:
>
> A common PT config is to just run it as a ring buffer in the background
> and only take the data out when something happens (sample, crash etc.)
>
> But the side band still needs to be logged and at arbitary times.
>
> So the PT wrapping will happen much more often than the perf wrapping.

So create two events, one for the PT stuff and one to track the
side-band stuff. We have a NOP event for just this purpose.


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