interpret the result of perf stat

[Peter Teoh]

On Tue, Oct 4, 2011 at 9:53 AM, Peter Teoh <htmldeveloper at gmail.com> wrote:

>
> On Sun, Oct 2, 2011 at 5:07 AM, Zheng Da <zhengda1936 at gmail.com> wrote:
> > Hello,
> >
> > I start to use perf to profile my program, but I'm not quite sure if I
> > understand some events.
>
> Firstly perf is using hardware to read these performance information.   So
> for intel CPU, depending on the different model, u can find the relevant
> information in the reference manual from Intel here:
>
> http://www.intel.com/Assets/en_US/PDF/manual/248966.pdf
>
> In particular, the various model of Intel CPU is listed in page xvii, and
> along with it are the various performance information u can extract out -
> the last item is the BUS information (B.6.10).
>
>
> > First, perf can profile bus cycles. Is it the bus cycles of FSB?
> > Second, what is task clock? It seems to me that task clock is the
>

task clock, from reading the implementation in kernel/events/core.c, i
suspect is a software event, not hardware.   Ie, it counts upon each task
switch.   To quote from core.c:

/*
 * Software event: task time clock
 */

static void task_clock_event_update(struct perf_event *event, u64 now)
{


More details here:

http://lwn.net/Articles/312720/


> > ticks used by a process. It should include the ticks used in the
> > kernel mode and the user space mode, as long as it is used in the
> > context of the process. I suppose it doesn't count the cycles used by
> > the interrupts such as page faults and softirq, even though the irqs
> > are caused by the process. Is it correct?
>

on the contrary, i think it should include, as to exclude these cycles does
entail stopping the hrtimer.....read into core.c further.


> >
> > Thanks,
> > Da
> >
> > _______________________________________________
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> >
>
>
>
> --
> Regards,
> Peter Teoh
>
>


-- 
Regards,
Peter Teoh
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