Messages in this thread | | | Subject | Re: [PATCH 04/12] perf_events: sync branch stack sampling with X86 precise_sampling | From | Peter Zijlstra <> | Date | Fri, 07 Oct 2011 12:37:59 +0200 |
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On Fri, 2011-10-07 at 12:34 +0200, Stephane Eranian wrote: > On Thu, Oct 6, 2011 at 7:25 PM, Peter Zijlstra <peterz@infradead.org> wrote: > > On Thu, 2011-10-06 at 16:49 +0200, Stephane Eranian wrote: > >> > >> On Intel X86 PERF_SAMPLE_BRANCH_STACK is implemented using LBR, > >> therefore both features must be coordinated as they may not > >> configure LBR the same way. > > > > Differently, you mean? Both wanting the same configuration seems fine. > > > No, I meant you can allow LBR + precise_sampling>1 ONLY when > users set LBR to record ALL branches and at the same priv levels. In > other words, > you're exposing the LBR content used by the fixup code.
Right.
> One could argue, that if LBR is set to filter certain branches, it may > also be okay, > it's just that you won't necessarily get the same number of successful > fixups. The > samples are tagged when fixups were successful, so that may also be an viable > option. Best effort given the content of the LBR. Depending on the > code, that might > be slightly better than dropping to precise_sampling=1 (no fixups).
Possible, but I imagine it might surprise some people.
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