linux-kernel - Re: [PATCH v2 1/4] KVM: PPC: Book3S HV: exit halt polling on need

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Message-ID: <CANRm+CxhnS8QovecA_cW-_kz2JK61+YHRrJBmsMS0Qkd+mFffA@mail.gmail.com>
Date:   Mon, 17 May 2021 08:58:17 +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 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 <dmatlack@...gle.com> wrote:
>
> On Wed, May 12, 2021 at 6:58 PM 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.
> >
> > 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>
> > ---
> > 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