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

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Date:   Wed, 10 Mar 2021 17:32:21 -0500
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...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 3/10/2021 5:25 PM, 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?
> 

Right, Perf doesn't use the "hybrid_cpu" in /proc/cpuinfo.

Thanks,
Kan