Re: Real-Time Preemption, -RT-2.6.10-rc2-mm3-V0.7.31-7

[Ingo Molnar <mingo@elte.hu>]

* Rui Nuno Capela <rncbc@rncbc.org> wrote:

> > the trace buffer is too small to capture a significant portion of the
> > xrun - i'd suggest for you to increase it from 4096-1 to 4096*16-1, to
> > be able to capture a couple of hundreds of millisecs worth of traces.
> >
> 
> and how I do that? Is it some /proc magic or its in the kernel configuration?

it's the MAX_TRACE define in kernel/latency.c.

but please try to the -31-10 kernel that i've just uploaded, it has a
number of tracer enhancements:

 - process name tracking. The new format is:

    bash- 3633 80000003 0.264ms (+0.000ms): idle_cpu (wake_idle)
    bash- 3633 80000003 0.264ms (+0.000ms): idle_cpu (wake_idle)
    bash- 3633 80000003 0.264ms (+0.000ms): find_next_bit (wake_idle)

  this makes it easier to identify which process does what. This feature 
  has no significant overhead in the tracer itself, all the hard work is
  done when /proc/latency_trace is read by the user.

 - /proc/sys/kernel/mcount_enabled flag: if disabled then 
   /proc/latency_trace will only contain 'custom' events, but no 
   per-function entries. This can be useful to trace really long 
   latencies, to get a rough idea of what is going on.

 - /proc/latency_trace atomicity. It was fundamentally non-atomic, due 
   to it being a 4K-granular file interface. Now the kernel has a second
   layer of saved-trace logic, which makes sure that the only time the
   trace is switched is when the header of the trace is read. I.e. when
   cp-ing or cat-ing /proc/latency_trace, no new trace info will be
   used. This change could solve some of the 'truncated traces'
   weirdnesses reported.

	Ingo