On Fri, Sep 27, 2019 at 04:27:02PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li <wanpen...@tencent.com>
>
> Don't waste cycles to shrink/grow vCPU halt_poll_ns if host
> side polling is disabled.
>
> Cc: Marcelo Tosatti <mtosa...@redhat.com>
> Signed-off-by: Wanpeng Li <wanpen...@tencent.com>
> ---
> virt/kvm/kvm_main.c | 28 +++++++++++++++-------------
> 1 file changed, 15 insertions(+), 13 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index e6de315..b368be4 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2359,20 +2359,22 @@ void kvm_vcpu_block(struct kvm_vcpu *vcpu)
> kvm_arch_vcpu_unblocking(vcpu);
> block_ns = ktime_to_ns(cur) - ktime_to_ns(start);
>
> - if (!vcpu_valid_wakeup(vcpu))
> - shrink_halt_poll_ns(vcpu);
> - else if (halt_poll_ns) {
> - 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)
> + if (!kvm_arch_no_poll(vcpu)) {
Can vcpu->halt_poll_ns be cached and used both here and in the similar
check above? E.g.:
unsigned int vcpu_halt_poll_ns;
vcpu_halt_poll_ns = kvm_arch_no_poll(vcpu) ? 0 : vcpu->halt_poll_ns;
if (vcpu_halt_poll_ns) {
...
}
> + if (!vcpu_valid_wakeup(vcpu))
> 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);
> - } else
> - vcpu->halt_poll_ns = 0;
> + else if (halt_poll_ns) {
> + 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);
> + } else
> + vcpu->halt_poll_ns = 0;
Not your code, but it'd be a good time to add braces to the 'if' and
'else'. Per Documentation/process/coding-style.rst:
Do not unnecessarily use braces where a single statement will do.
...
This does not apply if only one branch of a conditional statement is a single
statement; in the latter case use braces in both branches:
if (condition) {
do_this();
do_that();
} else {
otherwise();
}
> + }
>
> trace_kvm_vcpu_wakeup(block_ns, waited, vcpu_valid_wakeup(vcpu));
> kvm_arch_vcpu_block_finish(vcpu);
> --
> 2.7.4
>
