linux-kernel - Re: [PATCH V3 1/5] perf/core: Add PERF_SAMPLE_WEIGHT

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Date:   Fri, 5 Feb 2021 08:45:59 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
        Yao Jin <yao.jin@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>, maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH V3 1/5] perf/core: Add PERF_SAMPLE_WEIGHT_STRUCT



On 2/5/2021 5:43 AM, Namhyung Kim wrote:
> On Fri, Feb 5, 2021 at 12:24 AM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>>
>> On 2/4/2021 9:00 AM, Namhyung Kim wrote:
>>> Hi Kan,
>>>
>>> On Sat, Jan 30, 2021 at 2:25 AM Liang, Kan <kan.liang@...ux.intel.com> wrote:
>>> [SNIP]
>>>> diff --git a/include/uapi/linux/perf_event.h
>>>> b/include/uapi/linux/perf_event.h
>>>> index b15e344..c50718a 100644
>>>> --- a/include/uapi/linux/perf_event.h
>>>> +++ b/include/uapi/linux/perf_event.h
>>>> @@ -145,12 +145,14 @@ enum perf_event_sample_format {
>>>>           PERF_SAMPLE_CGROUP                      = 1U << 21,
>>>>           PERF_SAMPLE_DATA_PAGE_SIZE              = 1U << 22,
>>>>           PERF_SAMPLE_CODE_PAGE_SIZE              = 1U << 23,
>>>> +       PERF_SAMPLE_WEIGHT_STRUCT               = 1U << 24,
>>>>
>>>> -       PERF_SAMPLE_MAX = 1U << 24,             /* non-ABI */
>>>> +       PERF_SAMPLE_MAX = 1U << 25,             /* non-ABI */
>>>>
>>>>           __PERF_SAMPLE_CALLCHAIN_EARLY           = 1ULL << 63, /* non-ABI; internal use */
>>>>     };
>>>>
>>>> +#define PERF_SAMPLE_WEIGHT_TYPE        (PERF_SAMPLE_WEIGHT |
>>>> PERF_SAMPLE_WEIGHT_STRUCT)
>>>
>>> I'm not sure you want to expose it in the uapi header as it's not
>>> intended to be used IMHO.
>>>
>>
>> I'm not sure I understood, but it's indeed used in the tool patch set.
>>
>> https://lore.kernel.org/lkml/1612296553-21962-6-git-send-email-kan.liang@linux.intel.com/
> 
> Well, it's not a big deal.. but I just worried if some users might do
> 
>    event.attr.sample_type = PERF_SAMPLE_WEIGHT_TYPE;
> 

Yes, it's possible. For this case, Kernel returns -EINVAL.

Actually, even without the macro, users may still set PERF_SAMPLE_WEIGHT 
| PERF_SAMPLE_WEIGHT_STRUCT manually. We cannot control what a user 
sets. I don't think it's a problem as long as the kernel can handle it 
properly.

Thanks,
Kan