On 05/19/2016 11:26 AM, Wanpeng Li wrote:
I think in general a good idea to poll if a timer will expire soon.
Some patch comments:
Same for all non-x86 archs:
> +static inline unsigned int kvm_arch_timer_remaining(struct kvm_vcpu *vcpu) {}
A function returning int, without a return statement?
That gives at least a compiler warning.
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -78,6 +78,9 @@ module_param(halt_poll_ns_grow, uint, S_IRUGO | S_IWUSR);
> static unsigned int halt_poll_ns_shrink;
> module_param(halt_poll_ns_shrink, uint, S_IRUGO | S_IWUSR);
>
> +/* lower-end of message passing workload latency TCP_RR's poll time < 10us */
> +static unsigned int halt_poll_ns_base = 10000;
> +
> /*
> * Ordering of locks:
> *
> @@ -1966,7 +1969,7 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu)
> grow = READ_ONCE(halt_poll_ns_grow);
> /* 10us base */
> if (val == 0 && grow)
> - val = 10000;
> + val = halt_poll_ns_base;
> else
> val *= grow;
>
> @@ -2015,11 +2018,15 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> DECLARE_SWAITQUEUE(wait);
> bool waited = false;
> u64 block_ns;
> + unsigned int delta, remaining;
>
> + remaining = kvm_arch_timer_remaining(vcpu);
and now it causes undefined behaviour, no?
> start = cur = ktime_get();
> - if (vcpu->halt_poll_ns) {
> - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns);
> + if (vcpu->halt_poll_ns || (remaining < halt_poll_ns_base)) {
> + ktime_t stop;
>
> + delta = vcpu->halt_poll_ns ? vcpu->halt_poll_ns : remaining;
> + stop = ktime_add_ns(ktime_get(), delta);
> ++vcpu->stat.halt_attempted_poll;
> do {
> /*
>
So you avoid to shrink/grow for these cases? Probably makes sense
