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Subject: Re: [PATCH] perf/intel: Remove Perfmon-v4 counter_freezing support
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Kan Liang <kan.liang@linux.intel.com>, luwei.kang@intel.com,
        Thomas Gleixner <tglx@linutronix.de>, wei.w.wang@intel.com,
        Tony Luck <tony.luck@intel.com>,
        Stephane Eranian <eranian@google.com>,
        Mark Gross <mgross@linux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        linux-kernel@vger.kernel.org
References: <20201109021254.79755-1-like.xu@linux.intel.com>
 <20201110151257.GP2611@hirez.programming.kicks-ass.net>
 <20201110153721.GQ2651@hirez.programming.kicks-ass.net>
From:   Like Xu <like.xu@linux.intel.com>
Organization: Intel OTC
Message-ID: <11ba9e20-84eb-3ea5-5987-8357ae5af53f@linux.intel.com>
Date:   Mon, 16 Nov 2020 11:22:24 +0800
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Hi Peter,

On 2020/11/10 23:37, Peter Zijlstra wrote:
> -static int __init intel_perf_counter_freezing_setup(char *s)
> -{
> -	bool res;
> -
> -	if (kstrtobool(s, &res))
> -		return -EINVAL;
> -
> -	disable_counter_freezing = !res;
> -	return 1;
> -}
> -__setup("perf_v4_pmi=", intel_perf_counter_freezing_setup);

...

> Anyway, as it stands I think the whole counter_freezing thing is a
> trainwreck and it needs to go.

If you really want to drop the counter_freezing stuff, we also need
to clean it up in Documentation/admin-guide/kernel-parameters.txt:

	perf_v4_pmi=	[X86,INTEL]
			Format: <bool>
			Disable Intel PMU counter freezing feature.
			The feature only exists starting from
			Arch Perfmon v4 (Skylake and newer).

However someone may still need it based on the correct understanding
of "Freeze-on-Overflow" as Stephane said. How about renaming and 
documenting it instead of discarding it completely?

Our guest PEBS enabling patches does not completely depend on it
and we do not require the administrator to enable perf_v4_pmi for
guest PEBS.

Would you generously take a look at the perf part in this series?

Thanks,
Like Xu