From: Wanpeng Li <kernellwp@gmail.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>
Subject: Re: [PATCH] KVM: LAPIC: Recalculate apic map in batch
Date: Wed, 19 Feb 2020 08:47:56 +0800 [thread overview]
Message-ID: <CANRm+Cyx+J+YK8FzFBV8LRNPeCaXPc93vjFdpA0D_hA+wrpywQ@mail.gmail.com> (raw)
In-Reply-To: <87zhdg84n6.fsf@vitty.brq.redhat.com>
On Tue, 18 Feb 2020 at 20:24, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Wanpeng Li <kernellwp@gmail.com> writes:
>
> > From: Wanpeng Li <wanpengli@tencent.com>
> >
> > In the vCPU reset and set APIC_BASE MSR path, the apic map will be recalculated
> > several times, each time it will consume 10+ us observed by ftrace in my
> > non-overcommit environment since the expensive memory allocate/mutex/rcu etc
> > operations. This patch optimizes it by recaluating apic map in batch, I hope
> > this can benefit the serverless scenario which can frequently create/destroy
> > VMs.
> >
> > Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
>
> An alternative idea: instead of making every caller return bool and
> every call site handle the result (once) just add a
> KVM_REQ_APIC_MAP_RECALC flag or a boolean flag to struct kvm. I
> understand it may not be that easy as it sounds as we may be conunting
> on valid mapping somewhere before we actually get to handiling
Yes.
> KVM_REQ_APIC_MAP_RECALC but we may preserve *some*
> recalculate_apic_map() calls (and make it reset KVM_REQ_APIC_MAP_RECALC).
Paolo, keep the caller return bool or add a booleen flag to struct
kvm, what do you think?
Wanpeng
next prev parent reply other threads:[~2020-02-19 0:48 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-18 10:47 [PATCH] KVM: LAPIC: Recalculate apic map in batch Wanpeng Li
2020-02-18 12:24 ` Vitaly Kuznetsov
2020-02-19 0:47 ` Wanpeng Li [this message]
2020-02-25 8:07 ` Paolo Bonzini
2020-02-25 8:31 ` Wanpeng Li
2020-02-25 8:50 ` Paolo Bonzini
2020-02-25 7:55 ` Wanpeng Li
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