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

Cyrill Gorcunov
2010-02-15T20:32:37Z

On Mon, Feb 15, 2010 at 09:11:02PM +0100, Robert Richter wrote:
> On 08.02.10 21:45:04, Cyrill Gorcunov 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.
> >
> > The main problem in implementing P4 PMU is that it has much more
> > restrictions for event to MSR mapping. So to fit into current
> > perf_events model I made the following:
> >
> > 1) Event representation. P4 uses a tuple of ESCR+CCCR+COUNTER
> > as an "event". Since every CCCR register mapped directly to
> > counter itself and ESCR and CCCR uses only 32bits of their
> > appropriate MSRs, I decided to use "packed" config in
> > in hw_perf_event::config. So that upper 31 bits are ESCR
> > and lower 32 bits are CCCR values. The bit 64 is for HT flag.
> >
> > So the base idea here is to pack into 64bit hw_perf_event::config
> > as much info as possible.
> >
> > Due to difference in bitfields I needed to implement
> > hw_perf_event::config helper which unbind hw_perf_event::config field
> > from processor specifics and allow to use it in P4 PMU.
>
> If we introduce model specific configuration, we should put more model
> specific code in here and then remove
>
> u64 (*raw_event)(u64);
>
> in struct x86_pmu.
>

It seems we should still support raw_events, if I understand the idea
right -- raw_events could be used for say OProfile (if we are going
to substitute oprofile with perfevents subsystem). So the only
difference with other architectural events is that raw_event
need to be "packed" before being set into.

Putting/packing more specific code into config could make code
even more complex. Dunno Robert...

> > 3) I've started unbinding x86_schedule_events into per x86_pmu::schedule_events
> > and there I hit hardness in binding HT bit. Have to think...
>
> Instead of implemting x86_pmu.schedule_events() you should rather
> abstract x86_pmu_enable(). This will be much more flexible to
> implement other model spcific features.

But I would need collect events and so on -- ie code duplication
will be there. Or you mean something else?

>
> -Robert
>
> --
> Advanced Micro Devices, Inc.
> Operating System Research Center
> email: robert.richter@amd.com
>
-- Cyrill