Re: [PATCH RFC V3 0/3] kvm: Improving directed yield in PLE handler

[Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>]

On 07/13/2012 12:47 AM, Raghavendra K T wrote:
> Currently Pause Loop Exit (PLE) handler is doing directed yield to a
> random vcpu on pl-exit. We already have filtering while choosing
> the candidate to yield_to. This change adds more checks while choosing
> a candidate to yield_to.
>
> On a large vcpu guests, there is a high probability of
> yielding to the same vcpu who had recently done a pause-loop exit.
> Such a yield can lead to the vcpu spinning again.
>
> The patchset keeps track of the pause loop exit and gives chance to a
> vcpu which has:
>
>   (a) Not done pause loop exit at all (probably he is preempted lock-holder)
>
>   (b) vcpu skipped in last iteration because it did pause loop exit, and
>   probably has become eligible now (next eligible lock holder)
>
> This concept also helps in cpu relax interception cases which use same handler.

The patches are tested on x86 only since I don't have access to s390
machine. Please let me know if changes are ok on s390.