linux-kernel - Re: [PATCH 1/1] x86: Quark: Enable correct cache size/type reporting

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Message-ID: <20140929141727.GA19294@gmail.com>
Date:	Mon, 29 Sep 2014 16:17:27 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Bryan O'Donoghue <pure.logic@...us-software.ie>
Cc:	Dave Jones <davej@...hat.com>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] x86: Quark: Enable correct cache size/type reporting


* Bryan O'Donoghue <pure.logic@...us-software.ie> wrote:

> On 29/09/14 14:40, Dave Jones wrote:
> >On Mon, Sep 29, 2014 at 03:06:12AM +0100, Bryan O'Donoghue wrote:
> >  > Quark X1000 lacks cpuid(4). It has cpuid(2) but returns no cache
> >  > descriptors we can work with i.e. cpuid(2) returns
> >  > eax=0x00000001 ebx=0x00000000 ecx=0x00000000 edx=0x00000000
> >  >
> >  > Quark X1000 contains a 16k 4-way set associative unified L1 cache
> >  > with 256 sets
> >  >
> >  > This patch emulates cpuid(4) in a similar way to other x86
> >  > processors like AMDs which don't support cpuid(4). The Quark code
> >  > is based on the existing AMD code.
> >
> >This looks like it would work, but I wonder if it would be a lot
> >simpler to do something like what we do in centaur_size_cache()
> >which is the other case I recall where we had to override
> >the CPUs definition of cache size.
> 
> Hi Dave.
> 
> It's working alright :)
> 
> My feeling is that we'll probably end up with less changes/new code taking
> the approach of quirking.

OTOH, if the Quark quirk is a .legacy_cache_size callback, it 
will be compiled out on 64-bit kernels. With your patch it's 
unconditional.

So Dave's suggestion makes sense.

Thanks,

	Ingo
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