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

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Date:   Mon, 28 Jun 2021 08:00:05 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Greg KH <greg@...ah.com>
Cc:     kan.liang@...ux.intel.com, 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 6/27/2021 11:55 PM, Greg KH wrote:
> On Sun, Jun 27, 2021 at 09:30:53AM -0700, Andi Kleen wrote:
>>> Then do not break things by renaming the device name, as you all have
>>> now stated that this name is part of the user/kernel api.
>> The renaming comes from the fallback mode on future systems. In the fallback
>> mode the driver doesn't know the true name, so it has to use  the numeric
>> name. If you don't use the fallback mode and have the full driver then yes
>> you'll get the same names as always (or at least as they make sense for the
>> hardware).
>>
>> But we would like to have the fallback mode too to allow more people use
>> uncore monitoring, and that's where the need to for the second name comes
>> in.
> So then just always use the "fallback" name if that is going to be the
> name you have for this hardware device.  Why would you want it to be
> renamed later on to a "fancier" name if there is only going to be
> one-per-chipset-type anyway?

It's an ugly numeric name, difficult to use

perf stat -e uncore_0_2//

instead of

perf stat -e uncore_cha//

It wouldn't exactly be an improvement for the full driver.

-Andi