Re: preempt-rt, NUMA and strange latency traces

[Sébastien Dugué]

On Thu, 2006-02-09 at 15:02 -0500, Lee Revell wrote:
> On Thu, 2006-02-09 at 12:24 +0100, Sébastien Dugué wrote:
> > On Thu, 2006-02-09 at 01:04 -0500, Lee Revell wrote:
> > > On Wed, 2006-02-08 at 11:45 +0100, Sébastien Dugué wrote:
> > > > The more I think about it, the more I tend to believe it's hardware 
> > > > related. It seems as if the CPU just hangs for ~27 ms before
> > > > resuming processing. 
> > > 
> > > That would be an exceptionally long latency - you would probably notice
> > > it if the mouse froze, VOIP dropped out, ping stops, etc for 30ms.
> > > 
> > 
> >   It's a test machine and I use it remotely with console redirected so
> > no mouse, no RT applications aside from my silly nanosleep() loop. But 
> > I do notice that that test sometimes takes more time (ie when I get 
> > those weird latencies). 
> 
> Argh.  You would think the vendors would consider a 30ms delay
> unacceptable.  This is big enough to show up on an MRTG graph of ping
> times ferchrissake.
> 
> I guess the assumption is that most hardware will never be used for even
> soft RT work...
> 
> Lee
> 

  That may be but in that case I may be pushing it a bit far testing
that kind of box with realtime stuff.

  As a former hw designer I find it useful to have some hardware 
monitoring capabilities on a system but it should either not be so
intrusive or at least we should be able to disable it.

  Sébastien.



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