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From: Jim Mattson <jmattson@google.com>
To: "Li,Rongqing" <lirongqing@baidu.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kvm list <kvm@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"H . Peter Anvin" <hpa@zytor.com>, Borislav Petkov <bp@alien8.de>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Joerg Roedel <joro@8bytes.org>,
	Wanpeng Li <wanpengli@tencent.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>
Subject: Re: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers
Date: Mon, 27 Apr 2020 10:30:22 -0700	[thread overview]
Message-ID: <CALMp9eQrGuqzy_ZRu+qU3A7PRkoi8JHWFRpm---cMhp9+J4j8A@mail.gmail.com> (raw)
In-Reply-To: <fd2a8092edf54a85979e5781dc354690@baidu.com>

On Sat, Apr 25, 2020 at 8:24 PM Li,Rongqing <lirongqing@baidu.com> wrote:
>
>
>
> > -----邮件原件-----
> > 发件人: Paolo Bonzini [mailto:pbonzini@redhat.com]
> > 发送时间: 2020年4月25日 0:30
> > 收件人: Jim Mattson <jmattson@google.com>; Sean Christopherson
> > <sean.j.christopherson@intel.com>
> > 抄送: Peter Zijlstra <peterz@infradead.org>; Li,Rongqing
> > <lirongqing@baidu.com>; LKML <linux-kernel@vger.kernel.org>; kvm list
> > <kvm@vger.kernel.org>; the arch/x86 maintainers <x86@kernel.org>; H .
> > Peter Anvin <hpa@zytor.com>; Borislav Petkov <bp@alien8.de>; Ingo Molnar
> > <mingo@redhat.com>; Thomas Gleixner <tglx@linutronix.de>; Joerg Roedel
> > <joro@8bytes.org>; Wanpeng Li <wanpengli@tencent.com>; Vitaly Kuznetsov
> > <vkuznets@redhat.com>
> > 主题: Re: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers
> >
> > On 24/04/20 18:25, Jim Mattson wrote:
> > >> Assuming we're going forward with this, at an absolute minimum the
> > >> RDMSRs need to be wrapped with checks on host _and_ guest support for
> > >> the emulated behavior.  Given the significant overhead, this might
> > >> even be something that should require an extra opt-in from userspace to
> > enable.
> > >
> > > I would like to see performance data before enabling this unconditionally.
> >
> > I wouldn't want this to be enabled unconditionally anyway, because you need to
> > take into account live migration to and from processors that do not have
> > APERF/MPERF support.
> >
> > Paolo
>
> I will add a kvm parameter to consider whether enable MPERF/APERF emulations, and make default value to false

Wouldn't it be better to add a per-VM capability to enable this feature?

  reply	other threads:[~2020-04-27 17:30 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-24  5:08 [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers Li RongQing
2020-04-24 10:01 ` Peter Zijlstra
2020-04-24 14:46   ` Sean Christopherson
2020-04-24 16:25     ` Jim Mattson
2020-04-24 16:30       ` Paolo Bonzini
2020-04-26  3:24         ` 答复: " Li,Rongqing
2020-04-27 17:30           ` Jim Mattson [this message]
2020-04-27 19:10             ` Paolo Bonzini
2020-04-26  3:22     ` 答复: " Li,Rongqing
2020-04-26  8:30   ` Li,Rongqing

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