From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: Jesse Barnes <jesse.barnes@intel.com>, Howard Chu <hyc@symas.com>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: MTRR initialization
Date: Thu, 20 Sep 2007 08:03:31 -0700 [thread overview]
Message-ID: <200709200803.31795.jbarnes@virtuousgeek.org> (raw)
In-Reply-To: <p73d4wdal00.fsf@bingen.suse.de>
On Wednesday, September 19, 2007 11:50:23 pm Andi Kleen wrote:
> Jesse Barnes <jesse.barnes@intel.com> writes:
> > To do this in a nicer way (and be less vulnerable to similar BIOS
> > funkiness) the kernel really needs full PAT support. That should allow
> > WC over WB and WC over UC mappings to occur, at least if I'm
> > remembering the docs right...
>
> PAT only really helps for device driver performance optimizations.
> But if the basic WB MTRRs are wrong PAT cannot really salvage it.
Look at the original bug report. There's a bug WB region so any subsequent WC
mappings via the MTRRs won't work, so you need PAT to do WC (unless you want
to rewrite all your MTRR settings as Howard has to do now).
Seems like more and more machines are being setup this way, and until we have
PAT users will have to jump through hoops to get good performance.
Jesse
next prev parent reply other threads:[~2007-09-20 15:10 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-14 16:33 MTRR initialization Howard Chu
2007-09-14 17:12 ` Yinghai Lu
2007-09-16 16:08 ` Howard Chu
2007-09-16 17:53 ` Yinghai Lu
2007-09-16 18:40 ` Eric W. Biederman
2007-09-18 17:53 ` Howard Chu
2007-09-18 18:18 ` Eric W. Biederman
2007-09-19 21:52 ` Jesse Barnes
2007-09-20 6:50 ` Andi Kleen
2007-09-20 12:05 ` Avi Kivity
2007-09-20 12:10 ` Andi Kleen
2007-09-20 12:46 ` Avi Kivity
2007-09-20 15:03 ` Jesse Barnes [this message]
2007-09-20 17:08 ` Jesse Barnes
2007-09-22 0:27 ` Siddha, Suresh B
2007-09-22 0:46 ` Howard Chu
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