fast pixel transfers on late model Iris workstations

[baskett at SGI.COM]

In response to several posting about pixel transfer rates on Iris
workstations, I ran some experiments on our latest products.
Pixel access on the latest series of IRIS products has been improved
via new data paths to pixel memory and new library calls to do block
mode transfers on those new data paths.  The products involved are the
GT, GTX, and the Personal Iris.  Below is a table of results I obtained
last week by running a simple C program on some of the machines in my
building.  The numbers below are not the best or the worst you can get
and they are not the official specifications but they do give some idea
of the kind of results you can achieve and they do show moderatly high
pixel transfer rates.  Rates are all to the nearest .1 megapixels per
second.  The block size I used was moderate: 100 x 100 pixels.


GL routine      GT        GTX       Personal Iris

rectwrite       1.3       8.0       0.9

lrectwrite      1.0       5.7       4.4

rectread        0.6       3.0       0.6

lrectread       0.6       2.0       2.5


rectwrite transfers a vector of 16 bit numbers from main memory to
a rectangle of 12 bit color index mode pixels in frame buffer memory.
lrectwrite transfers a vector of 32 bit numbers from main memory to a
rectangle of 24 bit RGB mode pixels in frame buffer memory.  rectread
and lrectread are the corresponding inverse transfers.  There is also
rectcopy which will move a rectangle of pixels from one area of the
screen to another at high speed.  Users of the Personal Iris might
want to note that color index pixels can be transfered by lrectwrite
and lrectread for the best transfer rates.  Users of the GTX should note
that the transfer rates above are with the host memory pages locked in
main memory with the mpin system function to avoid per page overhead
that reduces the transfer rates.  The transfer rates on the Personal
Iris will be even better on future software and microcode releases of
this very new product.  Hope this helps.

Forest Baskett