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RE: Use of newer locking primitives...
- To: "paul@xxxxxxx" <paul@xxxxxxx>, "win-pv-devel@xxxxxxxxxxxxxxxxxxxx" <win-pv-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Martin Harvey <martin.harvey@xxxxxxxxxx>
- Date: Thu, 1 Sep 2022 09:25:24 +0000
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- Thread-topic: Use of newer locking primitives...
-----Original Message-----
From: Durrant, Paul <xadimgnik@xxxxxxxxx>
>> Ouch. Pause is one of the optional vmexit instructions. So you do an entire
>> vm-exit, when all you wanted to do is sit on your backside for a few
>> nanoseconds.
>>
> Well, arguably the guest is being a better citizen by exiting. If we really
> want to be a potential CPU hog then we could remove the yield.
Well, here's the thing - we might be less of a CPU hog by doing the pause, and
letting the HW decide whether it wants to do its conditional vmexit, via some
trap. The specs say what they say, but the HW implementors will know the
details of how many cycles everything takes, and one would hope that they've
put something smart in to decide whether a pause does in fact trap and vmexit.
One would hope that executing multiple pauses in a row would be enough of a
clue.
MH.
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