linux-kernel - Re: [Patch v4 07/13] perf/x86: Add constraint for guest perf metrics event

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Message-ID: <a34053f8-233f-3ea3-0f74-863f8de2e7b2@amd.com>
Date:   Tue, 3 Oct 2023 12:06:12 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Dapeng Mi <dapeng1.mi@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Like Xu <likexu@...cent.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>, kvm@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhang Xiong <xiong.y.zhang@...el.com>,
        Lv Zhiyuan <zhiyuan.lv@...el.com>,
        Yang Weijiang <weijiang.yang@...el.com>,
        Dapeng Mi <dapeng1.mi@...el.com>,
        Jim Mattson <jmattson@...gle.com>,
        David Dunn <daviddunn@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Manali Shukla <manali.shukla@....com>,
        Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [Patch v4 07/13] perf/x86: Add constraint for guest perf metrics
 event

On 02-Oct-23 5:59 PM, Peter Zijlstra wrote:
> On Fri, Sep 29, 2023 at 08:50:07PM +0530, Ravi Bangoria wrote:
>> On 29-Sep-23 5:23 PM, Peter Zijlstra wrote:
> 
>>> I don't think you need to go that far, host can use PMU just fine as
>>> long as it doesn't overlap with a vCPU. Basically, if you force
>>> perf_attr::exclude_guest on everything your vCPU can haz the full thing.
> 
> ^ this..
> 
>> How about keying off based on PMU specific KVM module parameter? Something
>> like what Manali has proposed for AMD VIBS? Please see solution 1.1:
>>
>> https://lore.kernel.org/r/3a6c693e-1ef4-6542-bc90-d4468773b97d@amd.com
> 
> So I hadn't read that, but isn't that more or less what I proposed
> above?

Yes, it's pretty much same as:

   "Like I wrote, all we need to do is ensure vCPU tasks will never have a
   perf-event scheduled that covers guest mode. Currently this would be
   achievable by having event creation for both:

    - CPU events without attr::exclude_guest=1, and
    - task events for vCPU task of interest without attr::exclude_guest=1

   error with -EBUSY or something."

Thanks,
Ravi