Re: [PATCH 0/5] perf: add support for capturing skid IP
From: Andi Kleen
Date: Fri Jun 16 2017 - 12:06:42 EST
On Thu, Jun 15, 2017 at 11:52:07PM -0700, Stephane Eranian wrote:
> On Thu, Jun 15, 2017 at 4:18 PM, Andi Kleen <ak@xxxxxxxxxxxxxxx> 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.