From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <ab02ca98fa4d062fa678f028c3785fc5@quanstro.net>
From: erik quanstrom <quanstro@quanstro.net>
Date: Wed, 16 Jan 2008 19:59:38 -0500
To: 9fans@cse.psu.edu
Subject: Re: [9fans] man is really slow on a terminal
In-Reply-To: <13426df10801161630q961f8dcu58c2901a420a71c1@mail.gmail.com>
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> 
> I hope, hope, hope that nobody is really setting up firmware to
> respond to PCIe reads of the framebuffer. I don't see how this could
> be.

to read directly from the framebuffer, the video memory in the card
would have to be directly attached to the pcie interface on the card.
i believe that would require a general memory bus & coherency protcol
arbitrating between memory, pcie, and the gpu.

(the old-fashioned solution to this was dual-ported ram.)

of course, this is speculation.  but i think that it's safely not as simple
as just reading video memory.

also, even with the mtrr the reads are not read combining.  it's uncachable
for reads, so it's 32bit pio.  

> >
> > as one data point, my pcie-based nvidia card raises windows much
> > more slowly than the older agp one that i have.  and the pcie card
> > has every advantage.  the agp card runs in a intel celery system.
> 
> What OS? are you sure this is not an os setup issue?

uh, plan 9.

- erik

p.s. i found this link from nvidia on how to make textures faster.
one thing they're concerned about is the *latency* of downloading
textures.  that might apply to reading the fb as well.

http://download.nvidia.com/developer/Papers/2005/Fast_Texture_Transfers/Fast_Texture_Transfers.pdf