Re: [PATCH 4/4] Convert irq notifiers lists to RCU locking.

Gregory Haskins
2009-07-13T13:44:49Z

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Michael S. Tsirkin wrote:
> On Mon, Jul 13, 2009 at 04:32:34PM +0300, Gleb Natapov wrote:
>
>> Yeah I understand that other RCU read section may introduce delays too.
>> The question is how big the delay may be.
>>
>
> I recall seeing the number "at least 3 jiffies" somewhere, but that
> might have changed since.
>
I think it is dependent on how you configure your kernel...but that
sounds ballpark for one of the worst-case types IIRC.

>
>> I don't think multiple
>> milliseconds delay in device de-assignment is a big issue though.
>>
>
> Right. My point was that since the sync is done under kvm lock, the
> guest can easily get blocked trying to get kvm lock meanwhile.
>

Yeah, that is really the biggest issue here, I agree. The delay in the
actual deassignment path is NBD.

Kind Regards,
-Greg

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