[linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

[Andrew Morton]

Paul Davis <paul at linuxaudiosystems.com> wrote:
>
> >OK, thanks.  The problem areas there are the timer-based route cache
> >flushing and reiserfs.
> >
> >We can probably fix the route caceh thing by rescheduling the timer after
> >having handled 1000 routes or whatever, although I do wonder if this is a
> >thing we really need to bother about - what else was that machine up to?
> 
> i have one concern about this that i talked to takashi about when we
> were in bordeaux. it seems to me that the ALSA xrun debug stuff is
> measuring things when the interrupt handler for the ALSA device
> executes and detects an xrun. if the handler itself was delayed, then
> the stack trace for its execution doesn't or might not show what
> caused the delay. this means, perhaps, that we need to be rather
> careful interpreting these traces.
> 

We can usually tell that from the trace.  If it points up into a busy piece
of code then it's pretty obvious what's happening.  If the trace is due to
a long irq-off time then it will point up into the offending
local_irq_enable().