Re: [uml-devel] scheduling anomaly on uml (was: -rt doesn't compile for UML)

[Ingo Molnar <mingo@elte.hu>]

* Miklos Szeredi <miklos@szeredi.hu> wrote:

> > how come UML idled for 30 msecs here, while the workload was 
> > supposed to be CPU-bound? It's not IO bound anywhere, right? No SMP 
> > artifacts either, right?
> 
> Yes.  The UML kernel is UP, and I don't think 'date' or 'bash' want to 
> do any disk I/O.
> 
> Could disk I/O be blocking the tty?  I think UML uses separate threads 
> for these, but I don't know the details.

even if the workload is fully CPU bound externally - internally a 
request to the external (CPU-bound) thread will look like an asynchonous 
request - so small amounts of idle time can be within UML, legitimately. 
(for the amount of time it takes for the external thread to service the 
request)

30 msecs already sounds a bit excessive (this is on your T60 with 
Core2Duo, right?), and 1-2 seconds noticeable latency is definitely 
excessive.

	Ingo

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