From: Jon Smirl <jonsmirl@gmail.com>
To: linux-fbdev-devel@lists.sourceforge.net, fbui@comcast.net
Subject: Re: can't access video memory?
Date: Sat, 10 Sep 2005 11:01:39 -0400 [thread overview]
Message-ID: <9e4733910509100801508140b4@mail.gmail.com> (raw)
In-Reply-To: <091020051443.548.4322F10400014A8E000002242207020653079A0D00@comcast.net>
On 9/10/05, fbui@comcast.net <fbui@comcast.net> wrote:
> > Zack Smith wrote:
> > > Does anyone know what might cause this?
On x86 the kernel is limited to 1GB of virtual address space. So
physical memory plus mapped video needs to total less than 1GB for
best performance.
Systems with 1GB of RAM or more want to minimize mapped VRAM. Anything
that is mapped over the minimum pushes kernel data structures out of
normal access and into highmem access which is significantly slower.
For example mapping a 512MB video card on a 1GB system knocks about
10% off from your system performance since it pushes 512MB of RAM into
highmem access mode.
The drivers aren't smart enough to look for less than 1GB of physical
memory and expand their mapped areas.
None of this applies from user space. There are no problems with
mapping the full card.
--
Jon Smirl
jonsmirl@gmail.com
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next parent reply other threads:[~2005-09-10 15:01 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <091020051443.548.4322F10400014A8E000002242207020653079A0D00@comcast.net>
2005-09-10 15:01 ` Jon Smirl [this message]
2005-09-10 20:32 ` can't access video memory? Antonino A. Daplas
2005-09-09 15:18 Zack Smith
2005-09-10 5:46 ` Antonino A. Daplas
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