Re: Understanding timestamps in perf.data

[Dennis Gnad <dennis.gnad@kit.edu>]

On 02.09.2015 15:43, David Ahern wrote:
> On 9/2/15 3:28 AM, Dennis Gnad wrote:
>> Hi,
>>
>> I am interested in timestamped performance counter data (with a
>> specified sampling rate) as there is supposed to be saved in perf.data
>> when I use "perf record -T".
>>
>> However, I don't understand the complete output of "perf report -D", and
>> can't figure out which parts of it are the timestamps. Is there any
>> documentation that I overlooked?
>>
>> Actually if it helps, I am only interested in the name/raw event, value,
>> and timestamp, without any code/library information. Maybe the
>> information on which CPU it is from (on a multicore) could be
>> interesting as well.
>>
>> Do I need to start looking into the code? Any good place to start? I
>> probably need to do this anyway, instead of parsing the really large
>> perf report -D output.
>>
>
> Use 'perf script' instead of 'perf report -D' to dump the samples.

OK, I really overlooked this. Thank you!

But now I am confused by that output. If I run for example:

$ perf record -F 100 -T -e cycles,cache-misses ./my_code

my understanding is, that at 100Hz, the values of the specified 
performance counters are read. But when I run:

$ perf script -f time,event
2001301.016880: cycles:
2001301.016883: cycles:
2001301.016885: cycles:
2001301.016886: cache-misses:
2001301.016887: cache-misses:
2001301.016889: cache-misses:
2001301.016890: cycles:
2001301.016925: cache-misses:
2001301.017000: cycles:
2001301.031339: cycles:
[..]

I don't get the values of the events, only that they "happened", which 
isn't that helpful if it is only sampled at a certain frequency. I also 
tried other options, but don't seem to be able to get the actually 
sampled values of the counters.

Any idea what am I missing? Much thanks in advance!