Re: nested KVM slower than QEMU with gnumach guest kernel

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On Mon, Nov 17, 2014 at 10:10:25AM +0100, Samuel Thibault wrote:
> Jan Kiszka, le Mon 17 Nov 2014 10:04:37 +0100, a écrit :
> > On 2014-11-17 10:03, Samuel Thibault wrote:
> > > Gleb Natapov, le Mon 17 Nov 2014 10:58:45 +0200, a écrit :
> > >> Do you know how gnumach timekeeping works? Does it have a timer that fires each 1ms?
> > >> Which clock device is it using?
> > > 
> > > It uses the PIT every 10ms, in square mode
> > > (PIT_C0|PIT_SQUAREMODE|PIT_READMODE = 0x36).
> > 
> > Wow... how retro. That feature might be unsupported - does user space
> > irqchip work better?
> 
> I had indeed tried giving -machine kernel_irqchip=off to the L2 kvm,
> with the same bad performance and external_interrupt in the trace.
> 
They are always be in the trace, but do you see them each ms or each 10ms
with user space irqchip?

--
			Gleb.
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