linux-kernel - RE: [PATCH V7 00/18] KVM: x86/pmu: Add *basic* support to enable guest PEBS via DS

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Date:   Mon, 28 Jun 2021 07:49:38 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Zhu, Lingshan" <lingshan.zhu@...el.com>,
        Liuxiangdong <liuxiangdong5@...wei.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>
CC:     "bp@...en8.de" <bp@...en8.de>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "Yang, Weijiang" <weijiang.yang@...el.com>,
        "kan.liang@...ux.intel.com" <kan.liang@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "like.xu.linux@...il.com" <like.xu.linux@...il.com>,
        "Fangyi (Eric)" <eric.fangyi@...wei.com>,
        Xiexiangyou <xiexiangyou@...wei.com>
Subject: RE: [PATCH V7 00/18] KVM: x86/pmu: Add *basic* support to enable
 guest PEBS via DS

On Friday, June 25, 2021 5:46 PM, Zhu, Lingshan wrote:
> > Only on the host?
> > I cannot use pebs unless try with "echo 0 > /proc/sys/kernel/watchdog"
> > both on the host and guest on ICX.
> Hi Xiangdong
> 
> I guess you may run into the "cross-map" case(slow path below), so I think you
> can disable them both in host and guest to make PEBS work.
> 

Hi Lingshan, could we also reproduce this issue?

If the guest's watchdog takes away the virtual fixed counter, this will schedule the guest PEBS to use virtual PMC0. With the fast path (1:1 mapping), I think physical PMC0 is likely to be available for the guest PEBS emulation if no other host perf events are running.

Best,
Wei