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  #1  
Old August 20th, 2011, 11:02
hsn hsn is offline
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Default Long standing ULE scheduler problem with CPU intensive tasks
ULE scheduler in 7.X and 8.X (maybe in 6 too) has one scenario where it performs really bad. I remember that oldest release of ULE worked in this scenario well (better than 4bsd) but all following ULE versions are really bad in this.

How to reproduce:
  1. run some CPU eating task on lowest priority (best for testing is distributed.net client, because it is included in ports)
  2. then compile something which is using autoconf ./configure script

You will notice huge performance drop due to background dnetc client. Compile (especially ./configure stuff) runs really slow. It should run on the same speed as without dnetc because intelligent scheduler will steal CPU time from dnetc in favor of compiling. Dnetc is running at nice level 20 after all.

ULE scheduler can be tuned via sysctl a bit but i was not able to do any significant improvement
Last edited by phoenix; August 22nd, 2011 at 17:31. Reason: Please format your posts!
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Old September 26th, 2011, 00:04
fidaj fidaj is offline
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Which CPU in your system where you done the tests?
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Old September 26th, 2011, 08:02
hsn hsn is offline
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single Intel (in vmware) and dualcore intel on real hw.
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Old September 26th, 2011, 08:16
fidaj fidaj is offline
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Quote:
Originally Posted by hsn View Post
single Intel (in vmware) and dualcore intel on real hw.
May cause performance degradation when the hyper-threading?
Try to disable hyper-threading and look at the changes ...
Code:
echo "machdep.hyperthreading_allowed=0" >> /boot/loader.conf
At one-core and dual-core processors performance on the ULE scheduler does not suit me too...
I had to use the scheduler for Core2Duo - 4BSD.
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Old September 26th, 2011, 08:17
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none of them supports HT. Did you tried my how-to repeat test?
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Old September 26th, 2011, 08:26
fidaj fidaj is offline
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Quote:
Originally Posted by hsn View Post
none of them supports HT. Did you tried my how-to repeat test?
I have a Core2Duo processor - it also does NOT support hyper-threading, but disabling hyper-threading allows the kernel to properly use the topology of my CPU...

I do not repeat your test, but I noticed the same problem with ULE on other tasks running on my laptop...
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Old September 26th, 2011, 09:25
fidaj fidaj is offline
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For ULE may have to do more and sysctl kern.sched.steal_htt=0 ...
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Old October 31st, 2011, 12:07
fidaj fidaj is offline
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Will it help in your case?
http://docs.freebsd.org/cgi/mid.cgi?...32817.35db5ccd
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  #9  
Old October 31st, 2011, 13:40
hsn hsn is offline
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steal_htt to 0 didn't make any difference.

I will try patch after it will get integrated in v10.
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