Re: [PATCH][retry 1] Add support for Pause Filtering to AMD SVM

Ingo Molnar
2009-05-11T14:15:10Z

* Avi Kivity <avi@redhat.com> wrote:

>> +static int pause_interception(struct vcpu_svm *svm, struct kvm_run
>> *kvm_run)
>> +{
>> + /* Simple yield */
>> + vcpu_put(&svm->vcpu);
>> + schedule();
>> + vcpu_load(&svm->vcpu);
>> + return 1;
>> +
>
> Ingo, will this do anything under CFS, or will CFS note that
> nothing has changed in the accounting and reschedule us
> immediately?

The scheduler will yield to another task only if the current task
has become ineligible. I.e schedule() is largely a NOP on
TASK_RUNNING tasks (i.e. here).

I.e. this is a somewhat poor solution as far as scheduling goes. But
i'm wondering what the CPU side does. Can REP-NOP really take
thousands of cycles? If yes, under what circumstances?

Ingo