From: Wanpeng Li <kernellwp@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Rik van Riel <riel@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
kvm <kvm@vger.kernel.org>, Wanpeng Li <wanpeng.li@hotmail.com>,
Ingo Molnar <mingo@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Frederic Weisbecker <fweisbec@gmail.com>,
Radim <rkrcmar@redhat.com>
Subject: Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug
Date: Tue, 7 Jun 2016 15:35:27 +0800 [thread overview]
Message-ID: <CANRm+Cy1iHnUUOgfoLmK=qqq3gmcTDi7mApLSrWF+pvVGw+qgQ@mail.gmail.com> (raw)
In-Reply-To: <3f6b30bc-d0a5-4169-f285-5d476b70119c@redhat.com>
2016-06-07 15:31 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> On 07/06/2016 03:24, Rik van Riel wrote:
>> On Mon, 2016-06-06 at 15:40 +0200, Paolo Bonzini wrote:
>>>
>>> On 02/06/2016 15:59, Rik van Riel wrote:
>>>>
>>>> If a guest is saved to disk and later restored (eg. after
>>>> a host reboot), or live migrated to another host, I would
>>>> expect to get totally disjoint steal time statistics from
>>>> the "new run" of the guest (which is the same run of the
>>>> guest OS).
>>> Why? The preexisting guest steal time is always added to by
>>> KVM, so the time won't restart from zero.
>>>
>>> Continuing the previous count on CPU hot-unplug followed by hot-plug
>>> is less obvious, but I think it's overall the right thing to do.
>>>
>>> In fact, I was going to test a patch this week as simple as this:
>>>
>>> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
>>> index eea2a6f72b31..1ef5e48b3a36 100644
>>> --- a/arch/x86/kernel/kvm.c
>>> +++ b/arch/x86/kernel/kvm.c
>>> @@ -301,8 +301,6 @@ static void kvm_register_steal_time(void)
>>> if (!has_steal_clock)
>>> return;
>>>
>>> - memset(st, 0, sizeof(*st));
>>> -
>>> wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) |
>>> KVM_MSR_ENABLED));
>>
>> By removing the memset from initial bootup allocation,
>> can't that cause the steal time to "increase by a ludicrous
>> amount" the very first time it is compared with the arch
>> independent value in the scheduler code?
>>
>> In other words, would removal of the memset result in still
>> requiring Wanpeng's patch?
>
> The percpu area is initialized to zero, isn't it?
Your proposal can fix the steal clock warp during guest cpu hotplug, I
will send out a new version later.
Regards,
Wanpeng Li
prev parent reply other threads:[~2016-06-07 7:35 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-02 11:57 [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug Wanpeng Li
2016-06-02 12:00 ` Peter Zijlstra
2016-06-02 13:59 ` Rik van Riel
2016-06-03 5:34 ` Wanpeng Li
2016-06-06 13:40 ` Paolo Bonzini
2016-06-06 22:42 ` Wanpeng Li
2016-06-07 1:24 ` Rik van Riel
2016-06-07 7:31 ` Paolo Bonzini
2016-06-07 7:35 ` Wanpeng Li [this message]
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