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Old 09-04-2004, 03:07 PM   #1
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Question Multiprocessor alternance


Hihoo! I'm very surprised, as i've compiled kernels for a P4 hyperthreading and for a true P2 multiprocessor, and, watching peacefully gkrellm monitor, i've seen that cpu's were working in alternance. Ex.: one at 80% and he other at 20%, or one at 99% and the other at 1%, and never both at 100%. So, as i can't sleep and eat since i've seen that, my only hope to understand this is you. Please, help me.
 
Old 09-05-2004, 04:26 PM   #2
guzzi
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hyperthreading

Hello


My experiance with the 2.4 series kernels is that cpu's don't share work loads evenly between them. I have heard that the 2.6 series kernels do share the load better.

On a dual hyperthreaded xeon system, I have only seen maximum use of all cpu's when running 4 seti@home processes at the same time. For routine daily activities like compiling kernels there is always a cpu or two that make nothing but heat.
 
Old 09-06-2004, 09:01 AM   #3
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Thank you. Any other experiences?
 
Old 09-06-2004, 09:14 AM   #4
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My (hyperthreaded) dual xeon box shows the same alternation.

When using 3 of the 4 available cpu's (seti@home), 3 out of the 4 cpu's are at 99-100% (most of the time). But, never the same 3 cpu's.

Example, running only seti@home:

Cpu0 : 0.0% user, 0.0% system, 100.0% nice, 0.0% idle
Cpu1 : 0.0% user, 0.0% system, 0.0% nice, 100.0% idle
Cpu2 : 0.0% user, 0.7% system, 99.3% nice, 0.0% idle
Cpu3 : 0.0% user, 0.7% system, 99.3% nice, 0.0% idle

And a few cycles later:

Cpu0 : 0.0% user, 0.0% system, 0.0% nice, 100.0% idle
Cpu1 : 0.0% user, 0.7% system, 99.3% nice, 0.0% idle
Cpu2 : 0.0% user, 0.3% system, 99.7% nice, 0.0% idle
Cpu3 : 0.0% user, 0.8% system, 99.2% nice, 0.0% idle

I did experiment with disabeling hyperthreading (2 'real' cpu's instead of 4 'virtual'). The overall performance is better with 4 cpu's (although not that much).

Did not try the 2.6 kernel yet, so cannot tell anything about that.
 
Old 09-07-2004, 05:57 AM   #5
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Thanks again.
 
Old 09-07-2004, 08:48 AM   #6
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yes 2.4 kernels suck big time at multiprocessor balancing

definitely use the latest 2.6 as all modern distros now are 2.6 ready
 
  


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