linux-kernel - Re: [PATCH V2 1/25] x86/cpufeatures: Enumerate Intel Hybrid Technology feature bit

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Date:   Wed, 10 Mar 2021 14:42:47 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     kan.liang@...ux.intel.com, peterz@...radead.org, mingo@...nel.org,
        linux-kernel@...r.kernel.org, acme@...nel.org, tglx@...utronix.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,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>
Subject: Re: [PATCH V2 1/25] x86/cpufeatures: Enumerate Intel Hybrid
 Technology feature bit

On Wed, 2021-03-10 at 14:25 -0800, Ricardo Neri wrote:
> On Wed, Mar 10, 2021 at 09:01:47PM +0100, Borislav Petkov wrote:
> > On Wed, Mar 10, 2021 at 11:46:44AM -0800, Ricardo Neri wrote:
> > > But this series provides the use case, right? Kan's patches
> > > handle PMU counters
> > > that may differ cross types of CPUs. In patch 2,
> > > get_hybrid_params()
> > > needs to check first if X86_FEATURE_HYBRID_CPU is enabled before
> > > querying the hybrid parameters. Otherwise, we would need to rely
> > > on the
> > > maximum level of CPUID, which may not be reliable.
> > 
> > On Wed, Mar 10, 2021 at 11:33:54AM -0800, Srinivas Pandruvada
> > wrote:
> > > We are working on changes to P-State driver for hybrid CPUs using
> > > this
> > > define. They are still work in progress.
> > > But this patch can be submitted later with our set of changes.
> > 
> > Answering to both with a single mail:
> > 
> > I don't have a problem with X86_FEATURE_HYBRID_CPU - I simply don't
> > want
> > to show "hybrid_cpu" in /proc/cpuinfo unless there's a valid use
> > case
> > for userspace to know that it is running on a hybrid CPU.
> 
> Ah, I get your point now. You would like to see
> 
> #define X86_FEATURE_HYBRID_CPU               (18*32+15) /* "" This
> part has CPUs of more than one type */
> 
> Right? Now your first comment makes sense.
> 
> Srinivas, Kan, I don't think we need to expose "hybrid_cpu" in
> /proc/cpuinfo, do we?
I don't see any need.

Thanks,
Srinivas


> 
> Thanks and BR,
> Ricardo