Re: [RFC] Add --show-total-period for perf annotate

From: Martin LiÅka
Date: Mon May 25 2015 - 03:46:14 EST


On 05/23/2015 06:08 AM, Andi Kleen wrote:
Martin LiÅka <mliska@xxxxxxx> writes:

I've been working on a new feature for perf annotate, which should be able to annotate
instructions with total spent time (compared to percentage usage).

Let's consider following use-case. You want to compare two different compilers
on the same code base and let's assume 90% of wall-time is spent in a single function.
Moreover, let's say that these compilers produce assembly of a totally different size.

In such case, it's very useful to get an approximation of spent time on a bunch of instructions,
which can be compared among other compilers. Otherwise, one has to somehow sum percentages and compare
it to size of a function.

perf diff does not handle this? Especially with the differential
profiling options it should.

It does not work if you, in my case, compare ICC and GCC, where ICC uses a different mangling
scheme for fortran modules. Moreover, situation can be more complicated if a compiler performs
a bit different inlining decisions.


@@ -623,6 +624,8 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
if (!target__none(&opts->target) && !opts->initial_delay)
perf_evlist__enable(rec->evlist);

+ t0 = rdclock();
+
/*
* Let the child rip
*/
@@ -692,6 +695,9 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
goto out_child;
}

+ t1 = rdclock();
+ walltime_nsecs = t1 - t0;

The walltime can be later computed by the difference of the first and
the last time stamp after sorting the events. So you don't need the new header.

-Andi


Good point. Can you please help me how to compute a function percentage usage in perf annotate ;) ?

Thanks,
Martin


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