Re: Information regarding the perf tool

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

On 31/10/13 17:48, Andi Kleen wrote:
>>    In fact, I expected that for each entry into the PEBS a handler
>> would be executed, but Intel documentations points that to use PEBS
>> the tool (here perf) needs to allocate space for multiple PEBS
>> entries, so the when the handler is invoked there may be multiple
>> entries in the buffer, which makes things a little more obscure.
>
> perf always uses threshold 1 for the PEBS buffer.
>
> But yes there is some delay until the handler executes, and the
> time stamp is only computed in the handler.
>


David, Andi,

   thank you for your valuable comments, they're really helpful.

   David, wrt to the clock, which actually calls local_clock() I'm a bit 
worried about the comment in sched/clock.c

  * Similar to cpu_clock() for the current cpu. Time will only be observed
  * to be monotonic if care is taken to only compare timestampt taken on the
  * same CPU.

   I'll rerun my experiments making sure that I pin the processes to a 
single CPU.

Again, thank you!

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