Re: [Xen-ia64-devel] SMP guest and itc

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

Le Vendredi 10 Février 2006 19:15, Magenheimer, Dan (HP Labs Fort Collins) a 
écrit :
> Just to briefly reiterate my opinion on the general
> timer tick issue:  The vast majority of timer ticks
> get immediately reflected to the currently executing
> domain.   Since ticks are very frequent (though recently
> reduced in Linux/ia64 from 1024/sec to 250/sec), there
> needs to be a "fast path" that can easily determine
> if this is a "immediately reflect" tick or not.  It
> shouldn't be necessary to go through all the save/restore
> overhead to call C and then march down linked
> lists only to determine that this is indeed one of the
> 99% of ticks that should be immediately reflected.
From a performance POV, I agree with you.  But this is an orthogonal issue!

> That said, I agree that Xen needs to pre-synchronize ITC
> for host SMP to work properly.  I don't think guest SMP
> for Linux will force ITC to be paravirtualized, but
> I guess Tristan will let us know if he discovers otherwise.
Currently this is my option: Xen pre-synchronize ITC and no more ITC 
virtualization is performed.

Tristan.


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