Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts

Kevin Hao
2013-05-10T14:12:13Z

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On Fri, May 10, 2013 at 08:07:00AM +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2013-05-09 at 16:27 -0500, Scott Wood wrote:
> > On 05/09/2013 07:37:42 AM, Benjamin Herrenschmidt wrote:
> > > On Thu, 2013-05-09 at 17:44 +0800, tiejun.chen wrote:
> > > >
> > > > Actually in the case GS=1 even if EE=0, EXT/DEC/DBELL still occur
> > > as I
> > > > recall.
> > >
> > > Only if directed to the hypervisor.
> >
> > This is always the case with KVM, right? At least on booke...
>
> Hrm, on A2 we could choose iirc. Well not DEC but EXT at least, I don't
> remember about DBELL.
>
> > > > > Case 1)
> > > > > -> Local_irq_disable() will set soft_enabled = 0
> > > > > -> Now Externel interrupt happens, there we set PACA_IRQ_EE in
> > > > irq_happened, Also clears EE in SRR1 and rfi. So interrupts are hard
> > > > disabled. No more other interrupt gated by MSR.EE can happen. Looks
> > > > like the idea here is to not let a device keep on inserting
> > > interrupt
> > > > till the interrupt condition on device is cleared, right?
> > >
> > > The external interrupt line is level sensitive normally, so we have to
> > > mask MSR:EE in that case or the interrupt would keep re-occurring
> > > (note
> > > that FSL has this concept of auto-acked interrupts via the on die MPIC
> > > for which you can potentially use PACA_IRQ_EE_EDGE instead and avoid
> > > having to mask MSR:EE).
> >
> > Note that if we do this, we can no longer leave the interrupt vector in
> > EPR, and would have to track (potentially multiple different) pending
> > external interrupts in software.
>
> Right, you can have a little queue in the PACA and leave EE disabled if
> it's full. You can probably get away with a queue of 1 though :-)

So I would assume you will not pick up these two patches, right?
http://patchwork.ozlabs.org/patch/235530/
http://patchwork.ozlabs.org/patch/235532/

Anyway it is more easier to enable the external proxy by using this method.
But if you insist, I can respin a patch to use the method you suggested
since it will definitely reduce the window where the irq is hard disabled.

Thanks,
Kevin

>
> Cheers,
> Ben.
>
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