From mboxrd@z Thu Jan  1 00:00:00 1970
From: Wei Wang <wei.w.wang@intel.com>
Subject: Re: [PATCH v4 04/10] KVM/x86: intel_pmu_lbr_enable
Date: Thu, 03 Jan 2019 15:22:07 +0800
Message-ID: <5C2DB81F.3000906@intel.com>
References: <1545816338-1171-1-git-send-email-wei.w.wang@intel.com> <1545816338-1171-5-git-send-email-wei.w.wang@intel.com> <CALMp9eRPvxPCnAnWr8+U98PzZLQ8LzeBRMyPk0qROKBzSzSnRQ@mail.gmail.com>
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Cc: LKML <linux-kernel@vger.kernel.org>,
        kvm list <kvm@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Andi Kleen <ak@linux.intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Kan Liang <kan.liang@intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        like.xu@intel.com, Jann Horn <jannh@google.com>,
        arei.gonglei@huawei.com
To: Jim Mattson <jmattson@google.com>
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On 01/03/2019 07:26 AM, Jim Mattson wrote:
> On Wed, Dec 26, 2018 at 2:01 AM Wei Wang <wei.w.wang@intel.com> wrote:
>> The lbr stack is architecturally specific, for example, SKX has 32 lbr
>> stack entries while HSW has 16 entries, so a HSW guest running on a SKX
>> machine may not get accurate perf results. Currently, we forbid the
>> guest lbr enabling when the guest and host see different lbr stack
>> entries.
> How do you handle live migration?

This feature is gated by the QEMU "lbr=true" option.
So if the lbr fails to work on the destination machine,
the destination side QEMU wouldn't be able to boot,
and migration will not happen.

Best,
Wei