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Message-ID: <1410378027.28990.268.camel@misato.fc.hp.com>
Subject: Re: [PATCH v2 3/6] x86, mm, asm-gen: Add ioremap_wt() for WT
From: Toshi Kani <toshi.kani@hp.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
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        Yigal Korman <yigal@plexistor.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Wed, 10 Sep 2014 13:40:27 -0600
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On Wed, 2014-09-10 at 11:29 -0700, Andy Lutomirski wrote:
> On Wed, Sep 10, 2014 at 9:51 AM, Toshi Kani <toshi.kani@hp.com> wrote:
 :
> > +#ifndef ARCH_HAS_IOREMAP_WT
> > +#define ioremap_wt ioremap_nocache
> > +#endif
> > +
> 
> This is a little bit sad.  I wouldn't be too surprised if there are
> eventually users who prefer WC or WB over UC if WT isn't available
> (and they'll want a corresponding way to figure out what kind of fence
> to use).

Right, this redirection is not ideal for the performance, but it is done
this way for the correctness.  WT & UC have strongly ordered writes, but
WB & WC do not.

Thanks,
-Toshi