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Message-ID: <1410385673.28990.313.camel@misato.fc.hp.com>
Subject: Re: [PATCH v2 2/6] x86, mm, pat: Change reserve_memtype() to handle
 WT
From: Toshi Kani <toshi.kani@hp.com>
Date: Wed, 10 Sep 2014 15:47:53 -0600
In-Reply-To: <5410C4F7.4080704@zytor.com>
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To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@amacapital.net>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Arnd Bergmann <arnd@arndb.de>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Juergen Gross <jgross@suse.com>, Stefan Bader <stefan.bader@canonical.com>, Henrique de Moraes Holschuh <hmh@hmh.eng.br>, Yigal Korman <yigal@plexistor.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

On Wed, 2014-09-10 at 14:39 -0700, H. Peter Anvin wrote:
> On 09/10/2014 02:27 PM, Andy Lutomirski wrote:
> >>
> >> That's possible, but the only benefit is that we can enable WT on
> >> pre-PAT systems, which I do not think anyone cares now...  WB & UC work
> >> on pre-PAT systems.  WC & WT need PAT.  I think this requirement is
> >> reasonable.
> > 
> > It might end up being a cleanup, though.  A whole bunch of
> > rarely-exercised if (!pat_enabled) things would go away.
> > 
> 
> Yes.  Don't think of it as PAT vs non-PAT.  Think of it as a specific
> set of cache types available on different processors.  The fact that you
> may have to frob an MSR to initialize it is almost trivial in comparison.

Right.

Thanks,
-Toshi

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