linux-kernel - Re: [PATCH v3 1/5] KVM: exit halt polling on need_resched() for both book3s and generic halt-polling

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Date:   Tue, 18 May 2021 20:03:16 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     David Matlack <dmatlack@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Ben Segall <bsegall@...gle.com>,
        Venkatesh Srinivas <venkateshs@...omium.org>,
        Paul Mackerras <paulus@...abs.org>,
        Suraj Jitindar Singh <sjitindarsingh@...il.com>
Subject: Re: [PATCH v3 1/5] KVM: exit halt polling on need_resched() for both
 book3s and generic halt-polling

On Tue, 18 May 2021 at 00:35, David Matlack <dmatlack@...gle.com> wrote:
>
> On Mon, May 17, 2021 at 7:01 AM Wanpeng Li <kernellwp@...il.com> wrote:
> >
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > 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. This
> > patch adds a helper function that to be shared between book3s and generic
> > halt-polling loop.
> >
> > Cc: Ben Segall <bsegall@...gle.com>
> > Cc: Venkatesh Srinivas <venkateshs@...omium.org>
> > Cc: Jim Mattson <jmattson@...gle.com>
> > Cc: David Matlack <dmatlack@...gle.com>
> > Cc: Paul Mackerras <paulus@...abs.org>
> > Cc: Suraj Jitindar Singh <sjitindarsingh@...il.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
>
> Reviewed-by: David Matlack <dmatlack@...gle.com>
>
> > ---
> > v2 -> v3:
> >  * add a helper function
> > v1 -> v2:
> >  * update patch description
> >
> >  arch/powerpc/kvm/book3s_hv.c | 2 +-
> >  include/linux/kvm_host.h     | 2 ++
> >  virt/kvm/kvm_main.c          | 9 +++++++--
> >  3 files changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> > index 28a80d240b76..360165df345b 100644
> > --- a/arch/powerpc/kvm/book3s_hv.c
> > +++ b/arch/powerpc/kvm/book3s_hv.c
> > @@ -3936,7 +3936,7 @@ static void kvmppc_vcore_blocked(struct kvmppc_vcore *vc)
> >                                 break;
> >                         }
> >                         cur = ktime_get();
> > -               } while (single_task_running() && ktime_before(cur, stop));
> > +               } while (kvm_vcpu_can_block(cur, stop));
> >
> >                 spin_lock(&vc->lock);
> >                 vc->vcore_state = VCORE_INACTIVE;
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 2f34487e21f2..bf4fd60c4699 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -1583,4 +1583,6 @@ static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu)
> >  /* Max number of entries allowed for each kvm dirty ring */
> >  #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
> >
> > +bool kvm_vcpu_can_block(ktime_t cur, ktime_t stop);
> > +
> >  #endif
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 6b4feb92dc79..c81080667fd1 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -2945,6 +2945,12 @@ update_halt_poll_stats(struct kvm_vcpu *vcpu, u64 poll_ns, bool waited)
> >                 vcpu->stat.halt_poll_success_ns += poll_ns;
> >  }
> >
> > +
> > +bool kvm_vcpu_can_block(ktime_t cur, ktime_t stop)
>
> nit: kvm_vcpu_can_poll() would be a more accurate name for this function.

Do it in v4. :)

    Wanpeng