Re: [RFC patch 1/2] sched: dynamically adapt granularity with nr_running

Ingo Molnar
2010-09-13T06:42:08Z

* Mike Galbraith <efault@gmx.de> wrote:

> On Sun, 2010-09-12 at 14:16 -0400, Mathieu Desnoyers wrote:

> > Or am I missing your point ?
>
> Yes and no. I'm pondering the parent, but by the same token, the
> vfork child shouldn't be penalized either.
>
> Does your latency go down drastically if you turn START_DEBIT off?
> Seems like it should. Perhaps START_DEBIT should not start a task
> further right than rightmost. I've done that before.
>
> maximum latency: 19221.5 µs
> average latency: 5159.0 µs
> missed timer events: 0
>
> maximum latency: 43901.0 µs
> average latency: 8430.1 µs
> missed timer events: 0
>
> Turning it off here cut latency roughly in half (i've piddled vfork
> though, but not completely). Limiting child placement to no further
> right than rightmost should help quite a bit.

Very interesting observation. Mathieu, mind testing Mike's suggestion
with wakeup-latency.c?

Thanks,

Ingo