Re: [RFC PATCH] check_preempt_tick should not compare vruntime with wall time

Mathieu Desnoyers
2010-09-13T18:19:28Z

* Ingo Molnar (mingo@elte.hu) wrote:
>
> * Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
>
> > * Linus Torvalds (torvalds@linux-foundation.org) wrote:
> > > On Mon, Sep 13, 2010 at 9:16 AM, Mathieu Desnoyers
> > > <mathieu.desnoyers@efficios.com> wrote:
> > > >
> > > > OK, the long IRC discussions we just had convinced me that the current scheme
> > > > takes things into account by adapting the granularity dynamically, but also got
> > > > me to notice that check_preempt seems to compare vruntime with wall time, which
> > > > is utterly incorrect. So maybe all my patch was doing was to expose this bug:
> > >
> > > Do you have latency numbers for this patch?
> >
> > Sure, see below,
> >
> > In addition to this patch, [...]
>
> Note, which is a NOP for your latency workload.
>
> > [...] I also used Peter's approach of reducing the minimum granularity
>
> Ok, that's the very first patch i sent yesterday morning - so we also
> have my numbers that it reduces latencies.
>
> To move things along i'll apply it with your Reported-by and Acked-by
> line, ok?
>
> We can also work on the other, more complex things after that, but first
> lets make some progress on the latency front ...

Yep, that's fine with me.

Thanks!

Mathieu

>
> Thanks,
>
> Ingo

--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.