From: Paolo Bonzini <pbonzini@redhat.com>
To: Wanpeng Li <kernellwp@gmail.com>, Marcelo Tosatti <mtosatti@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
LKML <linux-kernel@vger.kernel.org>, kvm <kvm@vger.kernel.org>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Linux PM" <linux-pm@vger.kernel.org>
Subject: Re: [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated physical CPUs are available
Date: Tue, 13 Aug 2019 09:55:16 +0200 [thread overview]
Message-ID: <b33a432f-b6a5-e9e8-a744-f29c21c69fd8@redhat.com> (raw)
In-Reply-To: <CANRm+CwtHBOVWFcn+6Z3Ds7dEcNL2JP+b6hLRS=oeUW98A24MQ@mail.gmail.com>
On 13/08/19 02:55, Wanpeng Li wrote:
>> I think KVM_HINTS_REALTIME is being abused somewhat.
>> It has no clear meaning and used in different locations
>> for different purposes.
>
> Now it disables pv queued spinlock, pv tlb shootdown, pv sched yield
> which are not expected present in vCPUs are never preempted for an
> unlimited time scenario.
Guest side polling definitely matches the purpose of KVM_HINTS_REALTIME.
While host-side polling is conditional on single_task_running, this is
obviously not true of guest-side polling.
The alternative would be to enable it only if KVM_FEATURE_POLL_CONTROL
is available, but I prefer Wanpeng's patch.
Paolo
>> For example, i think that using pv queued spinlocks and
>> haltpoll is a desired scenario, which the patch below disallows.
>
> So even if dedicated pCPU is available, pv queued spinlocks should
> still be chose if something like vhost-kthreads are used instead of
> DPDK/vhost-user. kvm adaptive halt-polling will compete with
> vhost-kthreads, however, poll in guest unaware other runnable tasks in
> the host which will defeat vhost-kthreads.
>
> Regards,
> Wanpeng Li
>
next prev parent reply other threads:[~2019-08-13 7:55 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1564643196-7797-1-git-send-email-wanpengli@tencent.com>
2019-08-01 16:51 ` [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated physical CPUs are available Rafael J. Wysocki
2019-08-01 16:54 ` Paolo Bonzini
2019-08-03 20:21 ` Marcelo Tosatti
2019-08-13 0:55 ` Wanpeng Li
2019-08-13 7:55 ` Paolo Bonzini [this message]
2019-08-26 20:40 ` Marcelo Tosatti
2019-08-27 0:43 ` Wanpeng Li
2019-08-28 8:35 ` Wanpeng Li
2019-08-28 8:45 ` Rafael J. Wysocki
2019-08-28 8:48 ` Wanpeng Li
2019-08-28 14:39 ` Marcelo Tosatti
2019-08-28 23:37 ` Rafael J. Wysocki
2019-08-29 12:04 ` Marcelo Tosatti
2019-08-29 12:16 ` Wanpeng Li
2019-08-29 12:53 ` Marcelo Tosatti
2019-08-29 14:39 ` Marcelo Tosatti
2019-08-28 14:48 ` Marcelo Tosatti
2019-08-28 14:52 ` Marcelo Tosatti
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