Anthony Liguori wrote:
> Dong, Eddie wrote:
>> Anthony Liguori wrote:
>>
>>> This should get moved to kvm_resched() since both VT/SVM would
>>> benefit from this.
>>>
>>>
>> I would suggest we just add similar code in SVM side. After we
>> optimize the MSR/VMCS register save/restore to skip for
>> those lightweight VM EXIT (handled by KVM). Giving up preemption
>> disable in kvm_resched means we need to do a full context
>> restore for host which is architecture specific.
>>
>
> The only time we'll give up preemption disable in kvm_resched is if
> need_resched() is true. This is fine since it's time to lose our time
> slice anyway.
>
> I was thinking that kvm_resched should look like:
>
> void kvm_resched(struct kvm_vcpu *vcpu)
> {
> if (need_resched()) {
> vcpu_put(vcpu);
> cond_resched();
> vcpu_load(vcpu);
> }
> }
Yes, this is true for today. But if the heavy MSR restore is only be
done for non lightweight VM Exit, that means
void kvm_resched(struct kvm_vcpu *vcpu)
{
if (need_resched()) {
/* restore host MSR register etc */
vcpu_put(vcpu);
cond_resched();
vcpu_load(vcpu);
}
}
Then the whole vmx_vcpu_run will look like:
vmx_vcpu_run()
{
/* save host MSR register etc. */
again: /* lightweight VM EXIT loop start here */
....
VM RESUME
kvm_vmx_return:
r = kvm_handle_exit()
if ( r > 0 ) {
...
...
if ( !need_resched()) goto again /* light weight
VM EXIT & no reschedule */
}
out: /* heavy weight VM EXIT or need_resched */
/* restore host MSR register etc. */
return r;
}
In this case, IOCTL return to Qemu will trigger scheduling at least.
Maybe I miss something.
thx,eddie
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