Re: [PATCH] KVM: Don't shrink/grow vCPU halt_poll_ns if host side polling is disabled
On Sat, 28 Sep 2019 at 01:24, Marcelo Tosatti wrote:
>
> On Fri, Sep 27, 2019 at 04:27:02PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li
> >
> > Don't waste cycles to shrink/grow vCPU halt_poll_ns if host
> > side polling is disabled.
> >
> > Cc: Marcelo Tosatti
> > Signed-off-by: Wanpeng Li
> > ---
> > 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)) {
> > + 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;
> > + }
> >
> > trace_kvm_vcpu_wakeup(block_ns, waited, vcpu_valid_wakeup(vcpu));
> > kvm_arch_vcpu_block_finish(vcpu);
> > --
> > 2.7.4
>
> Looks good.
I will add your ACK in v2.
Wanpeng
Re: [PATCH] KVM: Don't shrink/grow vCPU halt_poll_ns if host side polling is disabled
On Fri, 27 Sep 2019 at 22:42, Sean Christopherson
wrote:
>
> On Fri, Sep 27, 2019 at 04:27:02PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li
> >
> > Don't waste cycles to shrink/grow vCPU halt_poll_ns if host
> > side polling is disabled.
> >
> > Cc: Marcelo Tosatti
> > Signed-off-by: Wanpeng Li
> > ---
> > 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) {
> ...
> }
This is not correct, !kvm_arch_no_poll(vcpu) && vcpu->halt_poll_ns ==
0, you will stop grow.
>
> > + 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,
Not the truth. :)
>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();
> }
Will do in v2.
Wanpeng
Re: [PATCH] KVM: Don't shrink/grow vCPU halt_poll_ns if host side polling is disabled
On Fri, Sep 27, 2019 at 04:27:02PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li
>
> Don't waste cycles to shrink/grow vCPU halt_poll_ns if host
> side polling is disabled.
>
> Cc: Marcelo Tosatti
> Signed-off-by: Wanpeng Li
> ---
> 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)) {
> + 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;
> + }
>
> trace_kvm_vcpu_wakeup(block_ns, waited, vcpu_valid_wakeup(vcpu));
> kvm_arch_vcpu_block_finish(vcpu);
> --
> 2.7.4
Looks good.
Re: [PATCH] KVM: Don't shrink/grow vCPU halt_poll_ns if host side polling is disabled
On Fri, Sep 27, 2019 at 04:27:02PM +0800, Wanpeng Li wrote:
> From: Wanpeng Li
>
> Don't waste cycles to shrink/grow vCPU halt_poll_ns if host
> side polling is disabled.
>
> Cc: Marcelo Tosatti
> Signed-off-by: Wanpeng Li
> ---
> 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
>
