Re: Information regarding the perf tool

[Harald Servat <harald.servat@bsc.es>]

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On 31/10/13 19:22, David Ahern wrote:
> On 10/31/13, 11:23 AM, Harald Servat wrote:
>> Which is the relation between perf_clock() (or local_clock()) and
>> clock_gettime (CLOCK_MONOTONIC, ). Are they the same? If not, is there a
>> way to correlate them? Or alternatively, is it possible to call
>> local_clock() from the userland?
>
> We still do not have a means of correlating perf_clock to time-of-day,
> monotonic or any other clock source. Still trying.
>
> Pawell Moll has a couple of patches posted -- one uses an ioctl to get
> perf_clock timestamps the other makes perf_clock accessible through
> clock_gettime. See attached.
>
> David

Hello,

   thank you David! Those patches are great! I decided to access perf 
clock through clock_gettime because I'm more used to this call since I 
used it before.

   I understand that the patches are a bit hardcoded, right? I tried to 
#include "/usr/include/linux/time.h" after #include <time.h> but they 
seem to conflict. If I just extract the interesting bits (#define 
CLOCK_PERF) it seems to work. Is there a cleaner way to use this right now?

   JFTR, I have written a very small app that demonstrate the usage of 
this clock_gettime + perf (attached). It is very interesting to see that 
the difference between the monotonic and the perf clock is rather 
similar. However, as time goes by, at least in my machine, perf clock 
seems to advance at a faster pace than the monotonic clock.

Best regards.
-- 



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