Re: [RFC perf,x86] P4 PMU early draft

Cyrill Gorcunov
2010-02-09T06:54:45Z

On 2/9/10, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Cyrill Gorcunov <gorcunov@gmail.com> wrote:
>
>> Hi all,
>>
>> first of all the patches are NOT for any kind of inclusion. It's not ready
>>
>> yet. More likely I'm asking for glance review, ideas, criticism.
>
> A quick question: does the code produce something on a real P4? (possibly
> only running with a single event - but even that would be enough.)

not yet, a few code snippets need to be added into scheduling routine,
hope to finish this today evening

>
>> The main problem in implementing P4 PMU is that it has much more
>> restrictions for event to MSR mapping. [...]
>
> One possibly simpler approach might be to represent the P4 PMU via a maximum
> _two_ generic events only.
>

yeah, good idea!

> Last i looked at the many P4 events, i've noticed that generally you can
> create any two events. (with a few exceptions) Once you start trying to take
> advantage of the more than a dozen seemingly separate counters, additional
> non-trivial constraints apply.
>
> So if we only allowed a maximum of _two_ generic events (like say a simple
> Core2 has, so it's not a big restriction at all), we wouldnt have to map all
> the constraints, we'd only have to encode the specific event-to-MSR details.
> (which alone is quite a bit of work as well.)
>
> We could also use the new constraints code to map them all, of course - it
> will certainly be more complex to implement.
>

i thought about it, but i didn't like the result code ;) will think about it.

> Hm?
>
> Ingo
>