linux-kernel - Re: [RFC][PATCH 7/7] perf/annotate: Add branch stack / basic block information

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Message-ID: <20160708162733.GJ30909@twins.programming.kicks-ass.net>
Date:	Fri, 8 Jul 2016 18:27:33 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	acme@...nel.org, linux-kernel@...r.kernel.org, andi@...stfloor.org,
	eranian@...gle.com, jolsa@...nel.org,
	torvalds@...ux-foundation.org, davidcc@...gle.com,
	alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
	kan.liang@...el.com, khandual@...ux.vnet.ibm.com
Subject: Re: [RFC][PATCH 7/7] perf/annotate: Add branch stack / basic block
 information

On Fri, Jul 08, 2016 at 04:55:55PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > $ perf record --branch-filter u,any -e cycles:p ./branches 27
> > $ perf annotate branches
> 
> Btw., I'd really like to use this feature all the time, so could we please 
> simplify this somewhat via a subcommand, via something like:
> 
>   perf record branches ./branches 27
> 
> or if 'record' subcommands are not possible anymore:
> 
>   perf record --branches ./branches 27

So: perf record -b $workload, is basically enough and 'works'.

> 
> and in this case 'perf annotate' should automatically pick up the fact that the 
> perf.data was done with --branches - i.e. the highlighting should be automagic.

It does, or rather if the samples contain PERF_SAMPLE_BRANCH_STACK this
all gets automagically done.

The reason I did '--branch-filter u,any' is because this example is a very
tight loop that runs for many seconds and you get a fair number of
interrupts in it.

These interrupts result in branch targets and branches that don't exist,
and with such small code that really shows up.

For bigger code its not really an issue.

I've been thinking of filtering all targets and branches that are
smaller than 0.1% in order to avoid this, but so far I've just been
ignoring these things.