Re: [PATCH RFC dontapply 5/5] kvm_para: guest side for eoi avoidance

From: H. Peter Anvin
Date: Tue May 08 2012 - 11:45:45 EST

On 05/08/2012 08:28 AM, Gleb Natapov wrote:
> On Tue, May 08, 2012 at 05:26:55PM +0200, Paolo Bonzini wrote:
>> Il 23/04/2012 16:04, Michael S. Tsirkin ha scritto:
>>> +/* Our own copy of __test_and_clear_bit to make sure
>>> + * it is done with a single instruction */
>> Is this for microoptimization or correctness? If the latter, it does
>> not ensure anything without a "lock" prefix.
> It can't race with other vcpus, only with vmexit on the same vcpu.

That doesn't answer the question very well... I really don't understand
the point of having a private copy here.

I really, really don't want a bunch of private interfaces around. It
would be a lot better to define a test_and_{set,clear}_bit_local() in
<asm/bitops.h> which is defined to be local CPU atomic.


H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.

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