Re: Quake strangeness

Linus Torvalds (torvalds@cs.Helsinki.FI)
Wed, 6 Nov 1996 12:17:21 +0200 (EET)

On Tue, 5 Nov 1996, Bernd Bernie Meyer wrote:
>
> 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.
>
> I can't seem to make sense of this --- why is the local copy so much
> slower than the remote one? I tried running two local copies, and
> they both get app. 20fps, which is as expected. I tried running two
> local plus one remote copy, and the local ones became SLOOOOW again.
>
> Is this a scheduler thing, where the remote Quake process gets scheduled
> all the time due to network interrupts? But if so, why does top show all
> copies getting equal CPU time?

It's probably simply because the time-consuming part of quake is not so much
the actual drawing as the _calculations_ it is doing.

And with the remote copy, the load is a lot lower. With a local copy of
quake, the local load is pretty high, so the local quake binary has
trouble getting CPU for calculations, while the remote quake obviously
doesn't have that kind of performance problems..

Linus

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