Messages in this thread | | | Date | Tue, 06 Apr 2010 18:42:45 +0530 | From | Suresh Jayaraman <> | Subject | High priority threads causing severe CPU load imbalances |
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I have a simple test program that accepts number of threads(pthreads) to be created as a input. Each of these threads that gets created invokes a function which is just a infinite while loop. The main function after creating those threads goes in a infinite loop itself
My test machine is a Dual Core AMD Opteron(tm) 860 with 8 sockets(non-HT), I run this test program with number of threads == number of CPUs:
./loadcpu -t 16
I see 100% CPU utilization on almost all CPUs (via mpstat/htop/vmstat).
When the above threads are running, if I introduce a few high priority threads by doing:
nice -n -13 ./loadcpu -t 3
After a short while, I see a few CPUs becoming idle at ~0% utilization (the number of CPUs becoming idle equals roughly the number of high priority threads i.e. 3). When I stop the high priority threads, the CPU utilization comes back to normal i.e. ~100%.
This is reproducible on 2.6.32.10 stable kernel with all the recent all SMT fixes (I hope) and I think it would be reproducible in current upstream as well.
sched_mc_power_savings has been always set to 0.
I spent a while staring at the load balancing and the thread migration code, but could not figure out why this is happening. Would appreciate any pointers.
Thanks,
-- Suresh Jayaraman
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