From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753148AbcFFWmm (ORCPT <rfc822;w@1wt.eu>);
	Mon, 6 Jun 2016 18:42:42 -0400
Received: from mail-oi0-f53.google.com ([209.85.218.53]:34941 "EHLO
	mail-oi0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751164AbcFFWmk (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 6 Jun 2016 18:42:40 -0400
MIME-Version: 1.0
In-Reply-To: <b17566fa-1943-3bda-28f3-f6e21a424d9c@redhat.com>
References: <1464868639-8924-1-git-send-email-wanpeng.li@hotmail.com>
 <20160602120023.GC3190@twins.programming.kicks-ass.net> <1464875988.16365.119.camel@redhat.com>
 <b17566fa-1943-3bda-28f3-f6e21a424d9c@redhat.com>
From: Wanpeng Li <kernellwp@gmail.com>
Date: Tue, 7 Jun 2016 06:42:39 +0800
Message-ID: <CANRm+CyT=BtrBtNXJHThWKnzc4tzO1-dPeGX3S8cKtZTc3Phig@mail.gmail.com>
Subject: Re: [PATCH] sched/cputime: add steal clock warps handling during cpu hotplug
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>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

2016-06-06 21:40 GMT+08:00 Paolo Bonzini <pbonzini@redhat.com>:
>
>
> 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));
>         pr_info("kvm-stealtime: cpu %d, msr %llx\n",
>                 cpu, (unsigned long long) slow_virt_to_phys(st));

Thanks for the suggestion, I will try it today.

Regards,
Wanpeng Li