Re: Quake strangeness

Bernd (bmeyer@cs.monash.edu.au)
Thu, 7 Nov 1996 01:16:00 +1100 (EST)

>> Then, I got even sillier and started _another_ copy of Quake on the
>> ALPHA's local X-Server. And here the strange thing happened:
>>
>> While the copy that had to send all its data to the Pentium reached
>> 16fps, the local copy only reached about 6fps. According to top, they
>> both got equal CPU percentage; Also according to top (and vmstat), app.
>> half of the CPU-time was spent in system mode.
>
>It's probably simply because the time-consuming part of quake is not so much
>the actual drawing as the _calculations_ it is doing.

Uhm, I probably didn't make this completely clear:

_Both_ copies of quake are running on the ALPHA, running the same
executable on the same CPU. They both have to calculate every single
pixel on the ALPHA.

_One_ copy (the one I referred to as "local") copies each frame into
the X buffer, presumably via shared memory. X is taking about 5%
CPU load for this. The other copy (the "remote" one) instead is
sending the whole frame through two NE2000 cards to the Pentiums
X server.

Bow, with both copies doing the same calculations, and the remote copy
having to fight with the ethernet bottleneck, I would expect the
local copy to run faster than the remote one. The opposite is the
case, the remote copy is 2.5 times faster (16fps vs 6fps).

Bernie

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