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SubjectRe: [PATCH v6 2/3] KVM: dynamic halt_poll_ns adjustment
Date
On 9/3/15 2:09 AM, David Matlack wrote:
[...]
>> +
>> static int kvm_vcpu_check_block(struct kvm_vcpu *vcpu)
>> {
>> if (kvm_arch_vcpu_runnable(vcpu)) {
>> @@ -1929,6 +1963,7 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>> ktime_t start, cur;
>> DEFINE_WAIT(wait);
>> bool waited = false;
>> + u64 poll_ns = 0, wait_ns = 0, block_ns = 0;
>>
>> start = cur = ktime_get();
>> if (vcpu->halt_poll_ns) {
>> @@ -1941,10 +1976,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>> */
>> if (kvm_vcpu_check_block(vcpu) < 0) {
>> ++vcpu->stat.halt_successful_poll;
>> - goto out;
>> + break;
>> }
>> cur = ktime_get();
>> } while (single_task_running() && ktime_before(cur, stop));
>> +
>> + if (ktime_before(cur, stop)) {
> You can't use 'cur' to tell if the interrupt arrived. single_task_running()
> can break us out of the loop before 'stop'.
>
>> + poll_ns = ktime_to_ns(cur) - ktime_to_ns(start);
> Put this line before the if(). block_ns should always include the time
> spent polling; even if polling does not succeed.

How about something like:

@@ -1941,10 +1976,14 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
*/
if (kvm_vcpu_check_block(vcpu) < 0) {
++vcpu->stat.halt_successful_poll;
- goto out;
+ break;
}
cur = ktime_get();
} while (single_task_running() && ktime_before(cur, stop));
+
+ poll_ns = ktime_to_ns(cur) - ktime_to_ns(start);
+ if (ktime_before(cur, stop) && single_task_running())
+ goto out;
}

>
>> + goto out;
>> + }
>> }
>>
>> for (;;) {
>> @@ -1959,9 +1999,24 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
>>
>> finish_wait(&vcpu->wq, &wait);
>> cur = ktime_get();
>> + wait_ns = ktime_to_ns(cur) - ktime_to_ns(start);
>>
>> out:
>> - trace_kvm_vcpu_wakeup(ktime_to_ns(cur) - ktime_to_ns(start), waited);
>> + block_ns = poll_ns + wait_ns;
>> +
>> + if (halt_poll_ns) {
> If you want, you can leave this if() out and save some indentation.

Then we will miss the tracepoint.

Regards,
Wanpeng Li

>
>> + if (block_ns <= vcpu->halt_poll_ns)
>> + ;
>> + /* we had a long block, shrink polling */
>> + else if (vcpu->halt_poll_ns && block_ns > halt_poll_ns)
>> + shrink_halt_poll_ns(vcpu);
>> + /* we had a short halt and our poll time is too small */
>> + else if (vcpu->halt_poll_ns < halt_poll_ns &&
>> + block_ns < halt_poll_ns)
>> + grow_halt_poll_ns(vcpu);
>> + }
>> +
>> + trace_kvm_vcpu_wakeup(block_ns, waited);
>> }
>> EXPORT_SYMBOL_GPL(kvm_vcpu_block);
>>
>> --
>> 1.9.1
>>



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