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Old 04-13-06, 08:10 PM   #11
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Join Date: Apr 2006
Posts: 2
Default Re: even with 8756, minimal multitasking slows down glxgears performance

My own app is no small creature, but it's certainly not a CPU guzzler. Basically, there's a piece of software that consumes a lot (though not all) of the CPU. Then there's a graphical front-end that renders data exported to it over an IPC pipe. The front-end spends most of its time blocked on the pipe and/or rendering frames (and these are pretty simple frames -- low hundreds of polys). On every other machine I've used this is fine -- MLFQS (or whatever Linux is using) gives the front-end and every other app a chunk of time, and the CPU-hog gets what's left (which is usually 90+% of the CPU). With FC5+Nvidia drivers, this is apparently not the case.

Even if GLXgears is CPU-bound, that's not a complete explanation for this level of performance drain. Two CPU-bound processes should run reasonably, if at reduced performance; it should never be the case that one "hungry" process completely wastes another process (and not just transiently, but permanently). The exact same experiment (with GlxGears) described in my first post yields completely reasonable behavior and performance changes on two other non-FC5 machines with poorer hardware. On the machine I'm presently using, for instance, the CPU use of GlxGears drops to ~30% when another hog is on the processor, but on the other machine (which has nearly equivalent hardware) GlxGears is completely trounced -- dropping from 98% usage to < 1%. X still appears to run fine, though, as every other application/window works smoothly without issue. It seems to be isolated to programs using OpenGL.

I suspect this is a bug or misconfiguration of the drivers on my part, or a strange FC5 kernel issue (in which case, I should probably go bark up another tree ) In any case, I've certainly come to expect performance losses as a result of multitasking -- but this is way way outside of normal. If this is "normal", I'm going back to QNX where "multitasking" really means you can do more than one thing at a time. lol

Thanks for reading; bug file attached.

EDIT: apparently this other machine is 2.4Ghz; though that's still much faster than several others.
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