From: Jesse Barnes <jbarnes@engr.sgi.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Andrew Morton <akpm@osdl.org>,
linuxppc-dev list <linuxppc-dev@ozlabs.org>,
Linux Kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ppc32/64: Map prefetchable PCI without guarded bit
Date: Thu, 24 Mar 2005 08:54:45 -0800 [thread overview]
Message-ID: <200503240854.45741.jbarnes@engr.sgi.com> (raw)
In-Reply-To: <1111645464.5569.15.camel@gaston>
On Wednesday, March 23, 2005 10:24 pm, Benjamin Herrenschmidt wrote:
> While experimenting with framebuffer access performances, we noticed a
> very significant improvement in write access to it when not setting
> the "guarded" bit on the MMU mappings. This bit basically says that
> reads and writes won't have side effects (it allows speculation). It
> appears that it also disables write combining.
Doesn't pgprot_writecombine imply non-guarded, so can't you use it instead?
Either way, you'll probably want to fix fbmem.c as well and turn off
_PAGE_GUARDED?
Maybe it's time for a more generic call to support this stuff, both for
in-kernel mappings and ones that we export to userspace.
Jesse
next prev parent reply other threads:[~2005-03-25 6:29 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-24 6:24 [PATCH] ppc32/64: Map prefetchable PCI without guarded bit Benjamin Herrenschmidt
2005-03-24 16:54 ` Jesse Barnes [this message]
2005-03-24 16:55 ` Jesse Barnes
2005-03-25 22:23 ` Benjamin Herrenschmidt
2005-03-24 18:20 ` Segher Boessenkool
2005-03-25 22:26 ` Benjamin Herrenschmidt
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