Messages in this thread | | | Date | Tue, 7 Jan 2014 09:42:15 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units |
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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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