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

Ingo Molnar
2010-09-13T18:04:02Z

* 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 ...

Thanks,

Ingo