On 19/05/21 04:57, Wanpeng Li wrote:
Looks good. Hope Paolo can update the patch description when applying.:)
"In case of under-committed scenarios, vCPU can get scheduling easily,
kvm_vcpu_yield_to add extra overhead, we can observe a lot of races
between vcpu->ready is true and yield fails due to p->state is
TASK_RUNNING. Let's bail out in such scenarios by checking the length
of current cpu runqueue, it can be treated as a hint of under-committed
instead of guaranteeing accuracy. 30%+ of directed-yield attempts can
avoid the expensive lookups in kvm_sched_yield() in an under-committed
scenario. "
Here is what I used:
In case of under-committed scenarios, vCPUs can be scheduled easily;
kvm_vcpu_yield_to adds extra overhead, and it is also common to see
when vcpu->ready is true but yield later failing due to p->state is
TASK_RUNNING.
Let's bail out in such scenarios by checking the length of current cpu
runqueue, which can be treated as a hint of under-committed instead of
guarantee of accuracy. 30%+ of directed-yield attempts can now avoid
the expensive lookups in kvm_sched_yield() in an under-committed scenario.
Paolo
