Groups > linux.kernel > #1619007

Re: [PATCH v2 2/5] perf/x86/intel: Record branch type

From	Andi Kleen <ak@linux.intel.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 2/5] perf/x86/intel: Record branch type
Date	2017-04-07 20:00 +0200
Message-ID	<ttGkV-28n-1@gated-at.bofh.it> (permalink)
References	<ttshY-1au-3@gated-at.bofh.it> <ttshY-1au-13@gated-at.bofh.it> <ttDZM-w1-11@gated-at.bofh.it> <ttFoT-1r2-35@gated-at.bofh.it> <ttFRU-1SP-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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> > It's a somewhat common situation with partially JITed code, if you
> > don't have an agent. You can still do a lot of useful things.
> 
> Like what? How can you say anything about code you don't have?

For example if you combine the PMU topdown measurement, and see if it's
frontend bound, and then you see it has lots of forward conditionals,
then dynamic basic block reordering will help. If you have lots
of cross page jumps then function reordering will help. etc.

> > We found it useful to have this extra information during workload
> > analysis. Forward conditionals and page crossing jumps
> > are indications of frontend problems.
> 
> But you already have the exact same information in {to,from}, why would
> you need to repackage information already contained?

Without this patch, we don't know if it's conditional or something else.
And the kernel already knows this for its filtering, so it can as well
report it.

Right the CROSS_* and forward backward information could be computed
later.

-Andi

Thread

[PATCH v2 0/5] perf report: Show branch type Jin Yao <yao.jin@linux.intel.com> - 2017-04-07 05:00 +0200
  [PATCH v2 1/5] perf/core: Define the common branch type classification Jin Yao <yao.jin@linux.intel.com> - 2017-04-07 05:00 +0200
  [PATCH v2 2/5] perf/x86/intel: Record branch type Jin Yao <yao.jin@linux.intel.com> - 2017-04-07 05:00 +0200
    Re: [PATCH v2 2/5] perf/x86/intel: Record branch type Peter Zijlstra <peterz@infradead.org> - 2017-04-07 17:30 +0200
      Re: [PATCH v2 2/5] perf/x86/intel: Record branch type Andi Kleen <ak@linux.intel.com> - 2017-04-07 19:00 +0200
        Re: [PATCH v2 2/5] perf/x86/intel: Record branch type Peter Zijlstra <peterz@infradead.org> - 2017-04-07 19:30 +0200
          Re: [PATCH v2 2/5] perf/x86/intel: Record branch type Andi Kleen <ak@linux.intel.com> - 2017-04-07 20:00 +0200
            Re: [PATCH v2 2/5] perf/x86/intel: Record branch type "Jin, Yao" <yao.jin@linux.intel.com> - 2017-04-08 10:50 +0200

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