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From: Thomas Gleixner <tglx@linutronix.de>
To: "Luck\, Tony" <tony.luck@intel.com>
Cc: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>,
	x86@kernel.org, Borislav Petkov <bp@suse.de>,
	Ingo Molnar <mingo@kernel.org>, Len Brown <len.brown@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	linux-kernel@vger.kernel.org, Andy Lutomirski <luto@kernel.org>,
	"Peter Zijlstra \(Intel\)" <peterz@infradead.org>
Subject: Re: [PATCH 0/3] x86: Add initial support to discover Intel hybrid CPUs
Date: Sat, 03 Oct 2020 12:46:29 +0200	[thread overview]
Message-ID: <87lfgnd1tm.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201003021730.GA19361@agluck-desk2.amr.corp.intel.com>

On Fri, Oct 02 2020 at 19:17, Tony Luck wrote:

> On Sat, Oct 03, 2020 at 03:39:29AM +0200, Thomas Gleixner wrote:
>> On Fri, Oct 02 2020 at 13:19, Ricardo Neri wrote:
>> > Add support to discover and enumerate CPUs in Intel hybrid parts. A hybrid
>> > part has CPUs with more than one type of micro-architecture. Thus, certain
>> > features may only be present in a specific CPU type.
>> >
>> > It is useful to know the type of CPUs present in a system. For instance,
>> > perf may need to handle CPUs differently depending on the type of micro-
>> > architecture. Decoding machine check error logs may need the additional
>> > micro-architecture type information, so include that in the log.
>> 
>> 'It is useful' as justification just makes me barf.
>
> This isn't "hetero" ... all of the cores are architecturally the same.

The above clearly says:

>> > A hybrid part has CPUs with more than one type of micro-architecture.

Can you folks talk to each other and chose non-ambigous wording in
changelogs and cover letters?

> If CPUID says that some feature is supported, then it will be supported
> on all of the cores.

That's a different story.

> There might be some model specific performance counter events that only
> apply to some cores. Or a machine check error code that is logged in the
> model specific MSCOD field of IA32_MCi_STATUS. But any and all code can run
> on any core.

Ok. The perf side should be doable, IIRC we already have something like
that, but Peter should know better.

> Sure there will be some different power/performance tradeoffs on some
> cores. But we already have that with some cores able to achieve higher
> turbo frequencies than others.

Right, that's not a problem.

Thanks,

        tglx

  parent reply	other threads:[~2020-10-03 10:46 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-02 20:19 Ricardo Neri
2020-10-02 20:19 ` [PATCH 1/3] x86/cpufeatures: Enumerate hybrid CPU feature bit Ricardo Neri
2020-10-02 20:19 ` [PATCH 2/3] x86/cpu: Describe hybrid CPUs in cpuinfo_x86 Ricardo Neri
2020-10-02 20:34   ` Borislav Petkov
2020-10-02 21:02     ` Ricardo Neri
2020-10-02 21:03       ` Borislav Petkov
2020-10-02 23:41         ` Ricardo Neri
2020-10-02 20:19 ` [PATCH 3/3] x86/mce: include type of core when reporting a machine check error Ricardo Neri
2020-10-03  1:39 ` [PATCH 0/3] x86: Add initial support to discover Intel hybrid CPUs Thomas Gleixner
2020-10-03  2:17   ` Luck, Tony
2020-10-03  9:04     ` Borislav Petkov
2020-10-06  0:24       ` Ricardo Neri
2020-10-03 10:46     ` Thomas Gleixner [this message]
2020-10-03 14:39       ` Peter Zijlstra
2020-10-06  0:21       ` Ricardo Neri

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