linux-kernel - Re: [PATCH 2/2] amd: uncore: Get correct number of cores sharing last level cache

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Date:   Tue, 6 Jun 2017 19:45:02 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [PATCH 2/2] amd: uncore: Get correct number of cores sharing
 last level cache

On Tue, Jun 06, 2017 at 12:15:30PM +0200, Peter Zijlstra wrote:
> Maybe something like:
> 
> 	for (cache_level = 0; cache_level < 3; cache_level++) {
> 		cpuid_count(0x8000001d, cache_level, &eax, &ebx, &ecx, &edx);
> 
> 		if ((eax & 0x1f) == 0) /* EAX[0:4] gives cache type */

		if (!(eax & 0x1f))

> 			break;
> 
> 		prev_eax = eax;
> 	}
> 
> That way we'll not run off into the woods if CPUID goes funny (never
> trust a BIOS/virt monkey).

Yap, especially if there are CPUID functions with subleafs with holes in
them.

-- 
Regards/Gruss,
    Boris.

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