Re: [patch] voluntary-preempt-2.6.8.1-P2

Ingo Molnar
2004-08-19T07:48:43Z

* Thomas Charbonnel <thomas@undata.org> wrote:

> When entering check_preempt_timing, preempt_thresh was 0, and
> preempt_max_latency had been freshly reset to 100. It should have
> triggered this code :
>
> if (latency < preempt_max_latency)
> goto out;
>
> but for some reason it didn't (or there is a problem in the tracing
> code, not showing events that would have increased 'latency').

there is one case where we could 'miss' a new latency: when
/proc/latency_trace is accessed. For the duration of /proc/latency_trace
access, the updating of the max latency is stopped:

if (down_trylock(&max_mutex))
goto out;

this is not really a practical problem and fixing it would be quite
complex.

Ingo