linux-kernel - Re: [PATCH v4 5/6] KVM: x86/vPMU: Reuse perf_event to avoid unnecessary pmc_reprogram

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Date:   Thu, 14 Nov 2019 11:51:11 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Like Xu <like.xu@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>, Joerg Roedel <joro@...tes.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kan.liang@...el.com,
        wei.w.wang@...el.com, LKML <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH v4 5/6] KVM: x86/vPMU: Reuse perf_event to avoid
 unnecessary pmc_reprogram_counter

On Mon, 28 Oct 2019 at 21:06, Like Xu <like.xu@...ux.intel.com> wrote:
>
> The perf_event_create_kernel_counter() in the pmc_reprogram_counter() is
> a heavyweight and high-frequency operation, especially when host disables
> the watchdog (maximum 21000000 ns) which leads to an unacceptable latency

Why when host disables the watchdog,
perf_event_create_kernel_counter() is more heavyweight and
high-frequency operation?

    Wanpeng