Re: [patch] Latency Tracer, voluntary-preempt-2.6.8-rc4-O6

Ingo Molnar
2004-08-14T11:52:33Z

* James Courtier-Dutton <James@superbug.demon.co.uk> wrote:

> I have tested this for a day now, and I have noticed problems:
> 1)
> kernel syslog gets a record like this:
> > (default.hotplug/1470): 121 us critical section violates 100 us
> threshold.

> and the /proc/latency_trace gets:
> > preemption latency trace v1.0
> > -----------------------------
> > latency: 121 us, entries: 1032 (1032)
> > process: default.hotplug/1470, uid: 0
> > nice: -10, policy: 0, rt_priority: 0
> > =======>
> > 0.000ms (+0.000ms): page_address (kmap_high)
> > 0.000ms (+0.000ms): page_slot (page_address)
> > 0.000ms (+0.000ms): flush_all_zero_pkmaps (kmap_high)
> > 0.000ms (+0.000ms): set_page_address (flush_all_zero_pkmaps)

> Could the patch be adjusted to make the syslog and the
> /proc/latency_trace produce the same output?

We cannot include the full trace in the syslog - it's possibly thousands
of lines long.

> 2)
> I suspect that there is a problem with reiserfs, but when I detect a
> momentary hang in the system(mouse stops moving), no latency_trace appears.

well, the mouse could stop moving for a number of reasons. It's handled
via the X server and if the X server is preempted (for whatever reason)
then the mouse pointer isnt updated.

you could try to change the mouse IRQ to be non-threaded. Also, do you
have kernel_preemption set to 1? It defaults to 0.

Ingo