Messages in this thread | | | From | Stephane Eranian <> | Date | Fri, 16 Jun 2017 10:08:50 -0700 | Subject | Re: [PATCH 0/5] perf: add support for capturing skid IP |
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On Fri, Jun 16, 2017 at 9:06 AM, Andi Kleen <ak@linux.intel.com> wrote: > On Thu, Jun 15, 2017 at 11:52:07PM -0700, Stephane Eranian wrote: >> Andi, >> >> On Thu, Jun 15, 2017 at 4:18 PM, Andi Kleen <ak@linux.intel.com> wrote: >> >> Looking at this approach, the user interface is straightforward, >> >> implementation in the x86 code is a bit more hairy because of the way >> >> the branch_stack is captured, via the cpuc->lbr_entries. If you assume >> >> that SKID_IP cannot be used with any other branch stack mode, then it >> >> is easy. It becomes messy if you don't. >> > >> > That should be fine. After all if you have real LBRs you don't need >> > the skid IP. >> > >> Yes, you still do. This is not the same thing. LBR captures only taken branches. >> I care about taken AND non-taken branches and I don't want to sample on a >> non-taken event, assuming it is available. > > Ok that's a reasonable argument for reporting it separately, like > in your original patch. > Yeah, I think it is easier and more portable, especially on hardware with a PEBS-like mechanism but no branch buffer (like LBR). FYI, I did do a test implementation yesterday to evaluate the difficulty.
> -Andi
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