benh performance problem

hi all,
starting 2.6.0-test9-benh3 i noticed an increased system overhead on my ibook 500. Each process eats much more cpu time than in 2.4 or even vanilla 2.6.

gkrellm takes 1% instead of 0.1, xmms 5% instead of ~1% and so on. I benchmarked the lot with octave and it indeed runs ~10% slower on the benh kernels.
I would use vanilla 2.6.1 but it won't sleep/wake correctly (at all). All pre-2.6.0-test9-benh3 kernels worked fast but would't sleep/wake either. I tried to isolate the patch responsible but failed.
Has anybody come across similar behaviour?
greetings, M

Quoted 13 lines

Quoted 13 lines

hi all,
starting 2.6.0-test9-benh3 i noticed an increased system overhead on my ibook 500. Each process eats much more cpu time than in 2.4 or even vanilla 2.6.
gkrellm takes 1% instead of 0.1, xmms 5% instead of ~1% and so on. I benchmarked the lot with octave and it indeed runs ~10% slower on the benh kernels.
I would use vanilla 2.6.1 but it won't sleep/wake correctly (at all). All pre-2.6.0-test9-benh3 kernels worked fast but would't sleep/wake either. I tried to isolate the patch responsible but failed.
Has anybody come across similar behaviour?
greetings, M

I switched to HZ=1000, the userland procps utilities (like ps and top) tend to not properly deal with that, at least earlier versions, afaik.

I suspect it's just display crap.

Alos, you can find a more recent kernel than that My bk tree is currently at 2.6.2-rc3-ben1

Ben.

the benchmark i used shows a speedup back to the values i'm used to. The benchmark itself is an octave script the execution time of which i tested with different kernels under similar circumstances, so here are the details:

2.6.1-benh1, HZ=1000: timing=36.5s
2.6.1-benh1, HZ=100 : timing=32s

this is with X running and a lot more processes(not running). the weird thing is it executes slightly faster (on average) with pbbuttonsd off.
The machine is g3 500 ibook, the octave script is:

   tic;
     a = abs(randn(1500, 1500)/10);
     b = a';
     c= a*b;
     a = reshape(b, 750, 3000);
     b = a';
   timing=toc;

so lots of system calls and cache flushing is in order.

Mikolaj.

Quoted 3 lines · Mikolaj Krzewicki

2.6.1-benh1, HZ=1000: timing=36.5s
2.6.1-benh1, HZ=100 : timing=32s

The fact that pbbuttons makes a difference makes me think the interrupt handling is taking way too much time on your setup, and pbbuttons is loading the machine with PMU interrupts...

Not sure if I can fix any of this at this point without doing a major rewrite of the exception handling code, I suspect those CPUs don't like running in real mode and our exception handling happens mostly in that mode in ppc32...

pbbuttons is loading the machine? What about all those extra decrementer ticks? I assume benchmarks showed no performance degradation on some class of ppc32; what was the slowest system tested? For that matter, couldn't this hurt 4xx, 8xx(x), as well?

Perhaps HZ should be user-configurable? Although that doesn't help distributions who'd like one kernel to work everywhere... How does Linux handle increased HZ on old i386 anyways?

Quoted 4 lines

Not sure if I can fix any of this at this point without doing a major rewrite of the exception handling code, I suspect those CPUs don't like running in real mode and our exception handling happens mostly in that mode in ppc32...

I didn't realize CPUs go slower in real mode..?

Quoted 4 lines · Mikolaj Krzewicki

hi all,
starting 2.6.0-test9-benh3 i noticed an increased system overhead on my ibook 500. Each process eats much more cpu time than in 2.4 or even vanilla 2.6.

Quoted 8 lines

gkrellm takes 1% instead of 0.1, xmms 5% instead of ~1% and so on. I benchmarked the lot with octave and it indeed runs ~10% slower on the benh kernels.
I would use vanilla 2.6.1 but it won't sleep/wake correctly (at all). All pre-2.6.0-test9-benh3 kernels worked fast but would't sleep/wake either. I tried to isolate the patch responsible but failed.
Has anybody come across similar behaviour?
greetings, M

I switched to HZ=1000, the userland procps utilities (like ps and top) tend to not properly deal with that, at least earlier versions, afaik.

I suspect it's just display crap.