Re: [PATCH RFC V4 3/3] kvm: Choose better candidate for directedyield

From: Raghavendra K T
Date: Tue Jul 17 2012 - 22:31:07 EST

On 07/17/2012 02:39 PM, Raghavendra K T wrote:

if vcpu A is spinning for x% of its time and processing on the other,
then vcpu B will flip its dy_eligible for those x%, and not flip it when
it's processing. I don't understand how this is useful.

Suppose A is doing really good job and and has not done pause loop
exit, we will not touch it's dy_eligible flag. Also dy_eligible flag
will not prevent B doing yield_to to A.

Suppose A has started spinning in the beginning itself, it will do pause
loop exit if it crosses threshold, and we will now start toggling

Was that you were referring?

And it seems we may still have to set dy_eligible flag to false at the
beginning of vcpu_on_spin along with cpu_relax_intercepted = true, like
below, so that we do not have spill-over status from previous PL exits.

cpu_relax_intercepted = true;
dy_eligible = false;

cpu_relax_intercepted = false;

Let me know if that addresses your concern.

Thought you brought in is miraculous. taking care of not having spill-over dy_eligible status is needed for making algorithm technically more correct. will spin V5 with all these changes.

I guess this is an attempt to impose fairness on yielding, and it makes
sense to do this, but I don't know if this is the best way to achieve it.

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