Re: [PATCH 2/4] perf/x86/mbm: Store bytes counted for mbm during recycle

[Vikas Shivappa]

On Tue, 3 May 2016, Peter Zijlstra wrote:

> On Mon, Apr 25, 2016 at 02:12:09PM -0700, Vikas Shivappa wrote:
>
>
> > > start:
> > >      prev_count = read_hw_counter();
> >
> > I am assuming this means we keep the prev_count when event is initialized.
> > This is done in the mbm_init which calls update_sample with first parameter
> > set to true..
>
> No, when pmu::start() is called.
>
> > > read:
> > >      do {
> > >              prev = prev_count;
> > >              cur_val = read_hw_counter();
> > >              delta = cur_val - prev;
> > >      } while (local_cmpxchg(&prev_count, prev, cur_val) != prev);
> > >      count += delta;
>
> And this you do on pmu::{stop,read}()

Ok. We have same function for del and stop in cqm. Also we do count for cqm..
So we end up reading the 
counter every sched_out. We avoided this to not have the overhead. Also we have 
the overflow of mbm counters on top of this.

But I see how this can be done using the update_sample as the wrapper.

start:
  prev = update_sample(rmid) // reads the counter and takes care of overflow.

Basically replace the hw_counter call with the update_sample and also do the 
part thats done in the read in the overflow timer as well..

Will send an update.

Thanks,
Vikas