linux-kernel - Re: [PATCH 2/7] perf: Create a symlink for a PMU

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Date:   Fri, 25 Jun 2021 12:18:28 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Andi Kleen <ak@...ux.intel.com>, Greg KH <greg@...ah.com>
Cc:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org, eranian@...gle.com,
        namhyung@...nel.org, acme@...nel.org, jolsa@...hat.com
Subject: Re: [PATCH 2/7] perf: Create a symlink for a PMU

On 6/25/2021 11:57 AM, Liang, Kan wrote:
> 
> 
> On 6/25/2021 11:44 AM, Andi Kleen wrote:
>>
>>> We have an attribute "caps/pmu_name" for the core PMU. Maybe we 
>>> should add it for uncore PMU as well. For example,
>>>
>>> $ cat /sys/devices/uncore_type_0_0/caps/pmu_name
>>> cha_0
>>>
>>> Userspace tool can get clues about what type_0_0 is.
>>
>> It would break all the old tools, but I suppose it could work for 
>> updated tools.
>>
> 
> Right, users have to update their perf tool to use the new name, 
> uncore_cha_0.

I think the above example is misleading. Let me rephrase.
Here is what I'm planing to do in V2.

With the V2 platform-specific patch, uncore driver will only create a 
meaningful uncore name, e.g., uncore_cha_0.

An attribute "caps/pmu_name" is also created to indicate the previous 
name. For example,

$ cat /sys/devices/uncore_cha_0/caps/pmu_name
type_0_0

If any users use the old numeric name, they have to update either their 
script or a perf tool which supports "caps/pmu_name".

In the future, if the users already use a perf tool which supports 
"caps/pmu_name", nothing needs to be updated. The old numeric name 
should just work.

Thanks,
Kan