Messages in this thread | | | Date | Fri, 28 Jan 2000 08:26:39 +1000 (EST) | From | Peter Waltenberg <> | Subject | re: Strange scheduling behavoir in SMP (kernel 2.2.14) |
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> aflores@ditec.um.es wrote ============================= Hi,
I have a SMP machine with two Pentium III. In order to compare performance with other machines I began a simple test:
for (i=0;i<MAX_NUMBER;i++) for(j=0;j<MAX_NUMBER;j++) c=a*b; /* These variables could be integer or double */
Using kernel 2.2.12 with SMP support this simple program take more time in my machine than in a uniprocessor with K6-2 (the same problem appear in the last stable kernel 2.2.14) Using xosview application I discovered where the problem was. Instead of staying all the time in the same cpu, the process go from one cpu to other with a big performance lost.
Am I right?. Has been this problem solved in 2.3.x series?
Thanks a lot in advance. ===============================
No, it's still broken. Andrea has some patches for 2.2. 2.3 is still worse SMP than UP for anything CPU intensive.
I'm amazed that people are whinging about a phantom 5% in the scheduler when there's a real 100%+ to be gained by fixing this one.
It's a real bug. The current scheduler kicks running processes even when there's an idle CPU available. That means that heavy CPU use processes get ping-ponged across CPU's.
It's bad on a Dual Celeron with small caches, it must be a real killer on an 8 way Xeon ;)
Peter
---------------------------------- Peter Waltenberg Software Engineer IBM Software Group, Gold Coast
Phone: +61 7 5578 8933 Fax: +61 7 5578 8146 ----------------------------------
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