From: "H. Peter Anvin" <hpa@zytor.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Jerome Glisse <glisse@freedesktop.org>,
suresh.b.siddha@intel.com, venkatesh.pallipadi@intel.com,
thellstrom@vmware.com, airlied@linux.ie, currojerez@riseup.net,
linux-kernel@vger.kernel.org
Subject: Re: Uncool feature for TTM introduced by x86, pat: Use page flags to track memtypes of RAM pages
Date: Thu, 18 Feb 2010 09:38:01 -0800 [thread overview]
Message-ID: <4B7D7AF9.9060600@zytor.com> (raw)
In-Reply-To: <87aav65u9g.fsf@basil.nowhere.org>
On 02/18/2010 09:27 AM, Andi Kleen wrote:
> Jerome Glisse <glisse@freedesktop.org> writes:
>>
>> Can we modify the interface to support again changing from uc to wc
>> or wc to uc ? (i can try to do a patch for that).
>
> At least on Intel CPUs that support self-snoop (all modern
> ones) that should really be very cheap.
>
The UC/WC transition should be particularly trivial; I don't see any
reason it should have to go through any other procedure on *any* CPU --
selfsnoop shouldn't even figure into it, since neither UC nor WC
actually caches anything. For the WC->UC direction, all we should need
to do is to flush the write combiners; a simple wmb() will do that.
Self-snoop is about not having to flush something that can have been
cached, as is normally needed to do WB/WT/WP -> UC/WC.
-hpa
next prev parent reply other threads:[~2010-02-18 17:42 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-18 15:30 Uncool feature for TTM introduced by x86, pat: Use page flags to track memtypes of RAM pages Jerome Glisse
2010-02-18 16:35 ` Jerome Glisse
2010-02-18 18:46 ` Suresh Siddha
2010-02-18 17:27 ` Andi Kleen
2010-02-18 17:38 ` H. Peter Anvin [this message]
2010-02-18 20:27 ` Andi Kleen
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