linux-kernel - Re: [PATCH V2 20/25] perf/x86/intel: Add Alder Lake Hybrid support

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Date:   Thu, 11 Mar 2021 20:58:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, acme@...nel.org,
        tglx@...utronix.de, bp@...en8.de, namhyung@...nel.org,
        jolsa@...hat.com, ak@...ux.intel.com, yao.jin@...ux.intel.com,
        alexander.shishkin@...ux.intel.com, adrian.hunter@...el.com,
        Mark Rutland <mark.rutland@....com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH V2 20/25] perf/x86/intel: Add Alder Lake Hybrid support

On Thu, Mar 11, 2021 at 11:53:35AM -0500, Liang, Kan wrote:

> > > The "cpu_core" PMU is similar to the Sapphire Rapids PMU, but without
> > > PMEM.
> > > The "cpu_atom" PMU is similar to Tremont, but with different
> > > event_constraints, extra_regs and number of counters.

> > So do these things use the same event lists as SPR and TNT?
> 
> No, there will be two new event lists on ADL. One is for Atom core, and the
> other is for big core. They are different to SPR and TNT.

*sigh* how different?

> > Is there any
> > way to discover that, because AFAICT /proc/cpuinfo will say every CPU
> > is 'Alderlake', and the above also doesn't give any clue.
> > 
> 
> Ricardo once submitted a patch to expose the CPU type under
> /sys/devices/system/cpu, but I don't know the latest status.
> https://lore.kernel.org/lkml/20201003011745.7768-5-ricardo.neri-calderon@linux.intel.com/

Yeah, but that was useless, it doesn't list the Cores as
FAM6_SAPPHIRERAPIDS nor the Atom as FAM6_ATOM_TREMONT.

> > My desktop has: cpu/caps/pmu_name and that gives "skylake", do we want
> > the above to have cpu_core/caps/pmu_name give "sapphire_rapids" etc.. ?
> > 
> 
> I think current implementation should be good enough.
> 
> $ cat /sys/devices/cpu_atom/caps/pmu_name
> alderlake_hybrid
> 
> "alderlake_hybrid" tells the perf tool that it's Alder Lake Hybrid system.
> "cpu_atom" tells the perf tool that it's for Atom core.

Yeah, but then I have to ask Google wth those atoms and cores actually
are. Why not tell me upfront?

Since we're now working on it, we all know, but in 6 months time nobody
will remember and then we'll constantly have to look it up and curse
ourselves for not doing better.