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

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Date:	Mon, 25 May 2015 09:46:07 +0200
From:	Martin Liška <mliska@...e.cz>
To:	Andi Kleen <andi@...stfloor.org>
CC:	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>
Subject: Re: [RFC] Add --show-total-period for perf annotate

On 05/23/2015 06:08 AM, Andi Kleen wrote:
> Martin Liška <mliska@...e.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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