2021-05-13 02:01:20

by Wanpeng Li

Subject: [PATCH v2 1/4] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well

From: Wanpeng Li <[email protected]>

Inspired by commit 262de4102c7bb8 (kvm: exit halt polling on need_resched()
as well), CFS_BANDWIDTH throttling will use resched_task() when there is just
one task to get the task to block. It was likely allowing VMs to overrun their
quota when halt polling. Due to PPC implements an arch specific halt polling
logic, we should add the need_resched() checking there as well.

Cc: Ben Segall <[email protected]>
Cc: Venkatesh Srinivas <[email protected]>
Cc: Jim Mattson <[email protected]>
Cc: David Matlack <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Suraj Jitindar Singh <[email protected]>
Signed-off-by: Wanpeng Li <[email protected]>
---
v1 -> v2:
* update patch description

arch/powerpc/kvm/book3s_hv.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 28a80d2..6199397 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -3936,7 +3936,8 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
break;
}
cur = ktime_get();
- } while (single_task_running() && ktime_before(cur, stop));
+ } while (single_task_running() && !need_resched() &&
+ ktime_before(cur, stop));

spin_lock(&vc->lock);
vc->vcore_state = VCORE_INACTIVE;
--
2.7.4

2021-05-15 02:26:30

by David Matlack

Subject: Re: [PATCH v2 1/4] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well

On Wed, May 12, 2021 at 6:58 PM Wanpeng Li <[email protected]> wrote:
>
> From: Wanpeng Li <[email protected]>
>
> Inspired by commit 262de4102c7bb8 (kvm: exit halt polling on need_resched()
> as well), CFS_BANDWIDTH throttling will use resched_task() when there is just
> one task to get the task to block. It was likely allowing VMs to overrun their
> quota when halt polling. Due to PPC implements an arch specific halt polling
> logic, we should add the need_resched() checking there as well.
>
> Cc: Ben Segall <[email protected]>
> Cc: Venkatesh Srinivas <[email protected]>
> Cc: Jim Mattson <[email protected]>
> Cc: David Matlack <[email protected]>
> Cc: Paul Mackerras <[email protected]>
> Cc: Suraj Jitindar Singh <[email protected]>
> Signed-off-by: Wanpeng Li <[email protected]>
> ---
> v1 -> v2:
> * update patch description
>
> arch/powerpc/kvm/book3s_hv.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 28a80d2..6199397 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -3936,7 +3936,8 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> break;
> }
> cur = ktime_get();
> - } while (single_task_running() && ktime_before(cur, stop));
> + } while (single_task_running() && !need_resched() &&
> + ktime_before(cur, stop));

Consider moving this condition to a helper function that can be shared
between book3s and the generic halt-polling loop.

>
> spin_lock(&vc->lock);
> vc->vcore_state = VCORE_INACTIVE;
> --
> 2.7.4
>

2021-05-17 01:58:40

by Wanpeng Li

Subject: Re: [PATCH v2 1/4] KVM: PPC: Book3S HV: exit halt polling on need_resched() as well

On Sat, 15 May 2021 at 05:21, David Matlack <[email protected]> wrote:
>
> On Wed, May 12, 2021 at 6:58 PM Wanpeng Li <[email protected]> wrote:
> >
> > From: Wanpeng Li <[email protected]>
> >
> > Inspired by commit 262de4102c7bb8 (kvm: exit halt polling on need_resched()
> > as well), CFS_BANDWIDTH throttling will use resched_task() when there is just
> > one task to get the task to block. It was likely allowing VMs to overrun their
> > quota when halt polling. Due to PPC implements an arch specific halt polling
> > logic, we should add the need_resched() checking there as well.
> >
> > Cc: Ben Segall <[email protected]>
> > Cc: Venkatesh Srinivas <[email protected]>
> > Cc: Jim Mattson <[email protected]>
> > Cc: David Matlack <[email protected]>
> > Cc: Paul Mackerras <[email protected]>
> > Cc: Suraj Jitindar Singh <[email protected]>
> > Signed-off-by: Wanpeng Li <[email protected]>
> > ---
> > v1 -> v2:
> > * update patch description
> >
> > arch/powerpc/kvm/book3s_hv.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> > index 28a80d2..6199397 100644
> > --- a/arch/powerpc/kvm/book3s_hv.c
> > +++ b/arch/powerpc/kvm/book3s_hv.c
> > @@ -3936,7 +3936,8 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> > break;
> > }
> > cur = ktime_get();
> > - } while (single_task_running() && ktime_before(cur, stop));
> > + } while (single_task_running() && !need_resched() &&
> > + ktime_before(cur, stop));
>
> Consider moving this condition to a helper function that can be shared
> between book3s and the generic halt-polling loop.

Will do in the next version, thanks for review. :)

Wanpeng