linux-kernel - Re: [PATCH] perf/intel: Remove Perfmon-v4 counter

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Date:   Tue, 26 Jan 2021 19:35:03 +0800
From:   "Xu, Like" <like.xu@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Like Xu <like.xu@...ux.intel.com>, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Kan Liang <kan.liang@...ux.intel.com>, luwei.kang@...el.com,
        Thomas Gleixner <tglx@...utronix.de>,
        "Wang, Wei W" <wei.w.wang@...el.com>,
        Mark Gross <mgross@...ux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf/intel: Remove Perfmon-v4 counter_freezing support

On 2021/1/26 17:51, Paolo Bonzini wrote:
> On 11/11/20 03:42, Xu, Like wrote:
>> Hi Peter,
>>
>> On 2020/11/11 4:52, Stephane Eranian wrote:
>>> On Tue, Nov 10, 2020 at 7:37 AM Peter Zijlstra<peterz@...radead.org>  
>>> wrote:
>>>> On Tue, Nov 10, 2020 at 04:12:57PM +0100, Peter Zijlstra wrote:
>>>>> On Mon, Nov 09, 2020 at 10:12:37AM +0800, Like Xu wrote:
>>>>>> The Precise Event Based Sampling(PEBS) supported on Intel Ice Lake 
>>>>>> server
>>>>>> platforms can provide an architectural state of the instruction 
>>>>>> executed
>>>>>> after the instruction that caused the event. This patch set enables the
>>>>>> the PEBS via DS feature for KVM (also non) Linux guest on the Ice Lake.
>>>>>> The Linux guest can use PEBS feature like native:
>>>>>>
>>>>>>    # perf record -e instructions:ppp ./br_instr a
>>>>>>    # perf record -c 100000 -e instructions:pp ./br_instr a
>>>>>>
>>>>>> If the counter_freezing is not enabled on the host, the guest PEBS will
>>>>>> be disabled on purpose when host is using PEBS facility. By default,
>>>>>> KVM disables the co-existence of guest PEBS and host PEBS.
>> Thanks Stephane for clarifying the use cases for Freeze-on-[PMI|Overflow].
>>
>> Please let me express it more clearly.
>>
>> The goal of the whole patch set is to enable guest PEBS, regardless of
>> whether the counter_freezing is frozen or not. By default, it will not
>> support both the guest and the host to use PEBS at the same time.
>>
>> Please continue reviewing the patch set, especially for the slow path
>> we proposed this time and related host perf changes:
>>
>> - add intel_pmu_handle_guest_pebs() to __intel_pmu_pebs_event();
>> - add switch MSRs (PEBS_ENABLE, DS_AREA, DATA_CFG) to 
>> intel_guest_get_msrs();
>> - the construction of incoming parameters for 
>> perf_event_create_kernel_counter();
>>
>> I believe if you understand the general idea, the comments will be very 
>> valuable.
>
> What is the state of this work?  I was expecting a new version that 
> doesn't use counter_freezing.  However, I see that counter_freezing is 
> still in there, so this patch from Peter has never been applied.
>
> Paolo

Ah, now we have the v3 version on guest PEBS feature.
It does not rely on counter_freezing, but disables the co-existence of 
guest PEBS and host PEBS.
I am not clear about your attitude towards this co-existence.

There are also more interesting topics for you to review and comment.
Please check 
https://lore.kernel.org/kvm/20210104131542.495413-1-like.xu@linux.intel.com/