From: Andy Lutomirski <luto@amacapital.net>
To: Toshi Kani <toshi.kani@hp.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
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>
Subject: Re: [PATCH v2 3/6] x86, mm, asm-gen: Add ioremap_wt() for WT
Date: Wed, 10 Sep 2014 13:08:38 -0700 [thread overview]
Message-ID: <CALCETrXc-ecEt6mMuZee=MaoHD77XPWhjAJJUOgeXkcNZhC=Og@mail.gmail.com> (raw)
In-Reply-To: <1410378027.28990.268.camel@misato.fc.hp.com>
On Wed, Sep 10, 2014 at 12:40 PM, Toshi Kani <toshi.kani@hp.com> wrote:
> 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.
Fair enough. I think that this is unlikely to ever matter on x86, but
it might if NV-DIMMs end up used on another architecture w/o WT (or on
Xen, perhaps). Your code is certainly fine from a correctness POV.
Aside: WB writes are IIRC even more strongly ordered than WC.
>
> Thanks,
> -Toshi
>
--
Andy Lutomirski
AMA Capital Management, LLC
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next prev parent reply other threads:[~2014-09-10 20:09 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-10 16:51 [PATCH v2 0/6] Support Write-Through mapping on x86 Toshi Kani
2014-09-10 16:51 ` [PATCH v2 1/6] x86, mm, pat: Set WT to PA4 slot of PAT MSR Toshi Kani
2014-09-12 19:33 ` Konrad Rzeszutek Wilk
2014-09-12 20:45 ` Toshi Kani
2014-09-10 16:51 ` [PATCH v2 2/6] x86, mm, pat: Change reserve_memtype() to handle WT Toshi Kani
2014-09-10 18:26 ` Andy Lutomirski
2014-09-10 19:14 ` H. Peter Anvin
2014-09-10 19:30 ` Toshi Kani
2014-09-10 20:14 ` H. Peter Anvin
2014-09-10 20:30 ` Toshi Kani
2014-09-10 21:06 ` Andy Lutomirski
2014-09-10 21:11 ` Toshi Kani
2014-09-10 21:27 ` Andy Lutomirski
2014-09-10 21:25 ` Toshi Kani
2014-09-10 21:39 ` H. Peter Anvin
2014-09-10 21:47 ` Toshi Kani
2014-09-10 22:00 ` H. Peter Anvin
2014-09-10 23:24 ` Toshi Kani
2014-09-10 21:39 ` H. Peter Anvin
2014-09-10 20:31 ` Andy Lutomirski
2014-09-12 19:41 ` Konrad Rzeszutek Wilk
2014-09-10 16:51 ` [PATCH v2 3/6] x86, mm, asm-gen: Add ioremap_wt() for WT Toshi Kani
2014-09-10 18:29 ` Andy Lutomirski
2014-09-10 19:40 ` Toshi Kani
2014-09-10 20:08 ` Andy Lutomirski [this message]
2014-09-12 19:42 ` Konrad Rzeszutek Wilk
2014-09-10 16:51 ` [PATCH v2 4/6] x86, mm: Add set_memory_wt() " Toshi Kani
2014-09-12 19:47 ` Konrad Rzeszutek Wilk
2014-09-10 16:51 ` [PATCH v2 5/6] x86, mm, pat: Add pgprot_writethrough() " Toshi Kani
2014-09-12 19:47 ` Konrad Rzeszutek Wilk
2014-09-10 16:51 ` [PATCH v2 6/6] x86, pat: Update documentation for WT changes Toshi Kani
2014-09-10 18:30 ` Andy Lutomirski
2014-09-10 20:12 ` Toshi Kani
2014-09-10 20:29 ` Andy Lutomirski
2014-09-10 21:34 ` Toshi Kani
2014-09-15 21:19 ` Toshi Kani
2014-09-16 1:22 ` Andy Lutomirski
2014-09-16 16:52 ` Toshi Kani
2014-09-16 21:45 ` Yigal Korman
2014-09-16 22:13 ` Toshi Kani
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