linux-kernel - Re: [PATCH 0/5] perf: add support for capturing skid IP

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Message-ID: <20170615200205.GC4789@tassilo.jf.intel.com>
Date:   Thu, 15 Jun 2017 13:02:05 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Stephane Eranian <eranian@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "mingo@...e.hu" <mingo@...e.hu>,
        "Liang, Kan" <kan.liang@...el.com>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 0/5] perf: add support for capturing skid IP

On Thu, Jun 15, 2017 at 12:35:39PM -0700, Stephane Eranian wrote:
> On Thu, Jun 15, 2017 at 10:23 AM, Andi Kleen <ak@...ux.intel.com> wrote:
> > On Thu, Jun 15, 2017 at 09:44:07AM -0700, Stephane Eranian wrote:
> >> On Thu, Jun 15, 2017 at 8:10 AM, Andi Kleen <ak@...ux.intel.com> wrote:
> >> > On Thu, Jun 15, 2017 at 06:56:24AM -0700, Stephane Eranian wrote:
> >> >> This patchs adds a new sample record type called
> >> >> PERF_SAMPLE_SKID_IP. The goal is to record
> >> >> the unmodified interrupted instruction pointer (IP) as seen by
> >> >> the kernel and reflected in the machine state.
> >> >
> >> > Patches look reasonable for me.
> >> >
> >> > If you only cared about branches it would be more natural to model
> >> > it like a 1 entry LBR. That would make a lot more tooling work
> >> > automatically.
> >> >
> >> You'd still have to modify tooling to present correct column headers.
> >
> > Why? It's from/to?
> >
> Ah, yes you are right, but it is not clear to me how you would specify
> this cleanly with the interface.
> Especially in the case where this could be used for non-branch instructions.

Generally the skid ip is only interesting for instructions that have some kind of
control flow change, or an exception/interrupt.

So if it's interesting the headers would be correct.

Actually it's even correct for non control flow change, because the IP
moves from "FROM" to "TO" ... 

-Andi