Re: How how latent should non-preemptive scheduling be?

[Sitsofe Wheeler]

Ingo Molnar wrote:
> * Sitsofe Wheeler <sitsofe@xxxxxxxxx> wrote:
>
> > Ingo Molnar wrote:
> > > well, since they went away after you enabled CONFIG_PREEMPT=y, they are 
> > > definitely in-kernel latencies, not any external SMM latencies.
> > >
> > > I.e. they are inherently fixable. Could you enable:
> > >
> > >   CONFIG_DYNAMIC_FTRACE=y
> > >   CONFIG_FTRACE_MCOUNT_RECORD=y
> > >
> > > that should make the traces a lot more verbose - every kernel function  
> > > executed in the latency path will be logged. That way we'll be able to  
> > > say which one takes that long.
> > I do not appear to have the CONFIG_FTRACE_MCOUNT_RECORD option in 
> > 2.6.27rc7. Is it an option that is only in -tip ?
>
> yeah - it's a new ftrace feature queued up for v2.6.28.

I've been struggling to boot -tip/master - currently it blows up just 
after printing SLUB information saying:

BUG: unable to handle kernel NULL pointer dereference at 00000004
IP: [<c0120078>] account_system_time+0x48/0x120
*pde = 00000000
Thread overran stack, or stack corrupted
Oops: 0002 [#1] PREEMPT

--
Sitsofe | http://sucs.org/~sits/
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