Re: [PATCH RFC 2/2] kvm PLE handler: Choose better candidate fordirected yield

[Rik van Riel]

On 07/09/2012 02:20 AM, Raghavendra K T wrote:

> +bool kvm_arch_vcpu_check_and_update_eligible(struct kvm_vcpu *vcpu)
> +{
> +	bool eligible;
> +
> +	eligible = !vcpu->arch.plo.pause_loop_exited ||
> +			(vcpu->arch.plo.pause_loop_exited&&
> +			 vcpu->arch.plo.dy_eligible);
> +
> +	if (vcpu->arch.plo.pause_loop_exited)
> +		vcpu->arch.plo.dy_eligible = !vcpu->arch.plo.dy_eligible;
> +
> +	return eligible;
> +}

This is a nice simple mechanism to skip CPUs that were
eligible last time and had pause loop exits recently.

However, it could stand some documentation.  Please
add a good comment explaining how and why the algorithm
works, when arch.plo.pause_loop_exited is cleared, etc...

It would be good to make this heuristic understandable
to people who look at the code for the first time.

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