Re: [patch 3/4] KVM: introduce irq_lock, use it to protect ioapic

Avi Kivity
2009-05-26T11:33:35Z

Marcelo Tosatti wrote:
> On Sun, May 24, 2009 at 05:10:07PM +0300, Avi Kivity wrote:
>
>> Marcelo Tosatti wrote:
>>
>>> Subject says it all.
>>>
>>>
>> I hate those changelogs. I guess Subject never reviews code.
>>
>> You might put some evidence that we're suffering from contention here
>> (I'm very willing to believe it, but hard evidence is better).
>>
>
> Don't have any evidence yet, the main purpose of the split is to fix the
> deadlock.
>

You might have said that.

> But, with the data we have so far, slots_lock and kvm->lock will cause
> significant cache bouncing on EPT hardware (with measurements on shadow
> mmu_lock is #1 offender).
>

Well, mmu_lock is probably contended, which is much worse than just
cache bouncing.

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