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From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: "Luck, Tony" <tony.luck@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	x86@kernel.org, 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: Mon, 5 Oct 2020 17:24:04 -0700	[thread overview]
Message-ID: <20201006002404.GB6041@ranerica-svr.sc.intel.com> (raw)
In-Reply-To: <20201003090413.GB14035@zn.tnic>

On Sat, Oct 03, 2020 at 11:04:29AM +0200, Borislav Petkov wrote:
> On Fri, Oct 02, 2020 at 07:17:30PM -0700, Luck, Tony 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.
> 
> But it says above "A hybrid part has CPUs with more than one type of
> micro-architecture."
> 
> So which is it?

Yes, even though they have different micro-architectures, all instructions and
features will be the same across CPUs.

> 
> > If CPUID says that some feature is supported, then it will be supported
> > on all of the cores.
> 
> Ok.
> 
> > There might be some model specific performance counter events that only
> > apply to some cores.
> 
> That sounds like the perf counter scheduling code would have to pay
> attention to what is supported. I think we have some functionality for
> that due to some AMD parts but I'd prefer if Peter comments here.
> 
> > 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.
> 
> As long as that is consumed only by userspace I guess that's ok. The
> moment someone starts to want to differentiate on what kind of CPU
> kernel code runs and acts accordingly, then it becomes ugly so we better
> hash it out upfront.

We are not planning to implement changes as such.

Thanks and BR,
Ricardo

  reply	other threads:[~2020-10-06  0:45 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 [this message]
2020-10-03 10:46     ` Thomas Gleixner
2020-10-03 14:39       ` Peter Zijlstra
2020-10-06  0:21       ` Ricardo Neri

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