I see it works, wow, but I don’t quite understand why, although I’m rusty on
this kind of thing. Why do they do byte updates at all ? At 32 bits/pixel,
every pixel’s a dword anyway.
Alberto.
-----Original Message-----
From: Loren Wilton [mailto:xxxxx@earthlink.net]
Sent: Friday, October 03, 2003 10:20 AM
To: Windows System Software Devs Interest List
Subject: [ntdev] Re: Writing to Overlay from DPC is slower than from a pp
I’d be curious to hear whether this helps, I have this nagging feeling
that
write combine doesn’t help video performance that much, but I may be
wrong.
On the contrary. For normal video output, NT tries to set up the video area
as WC. The majority of the screen update is done by byte output to the
video card buffer, and the WC upgrade to 16 or 32 bit or larger transfers to
match whatever size will burst on the PCI interface to the video card helps
enormously. Turning off WC on the video card memory can easily slow down
rendering by something like a factor of 10 or so, and hugely increases the
bus traffic. It also hugely increases the processor time spent rendering
video.
There is a registry key someplace that can be used to disable WC setup of
the video area. Don’t recall what it is offhand, although I think there is
a KB article on it. We use it on the ES7000 server series since the
hardware doesn’t support write combining. The result is a real fast server
with real slow video. Not a recommended game platform… 
Loren
Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256
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