On 05/23/2015 06:08 AM, Andi Kleen wrote:
Martin Liška <mli...@suse.cz> 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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