Messages in this thread | | | Subject | Re: [PATCH v4 2/5] KVM: X86: Bail out of direct yield in case of under-committed scenarios | From | Paolo Bonzini <> | Date | Mon, 24 May 2021 15:42:30 +0200 |
| |
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
| |