Messages in this thread | | | Date | Wed, 21 Nov 2007 21:58:10 -0500 | From | Jie Chen <> | Subject | Re: Possible bug from kernel 2.6.22 and above |
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Simon Holm Thøgersen wrote: > ons, 21 11 2007 kl. 20:52 -0500, skrev Jie Chen:
> There is a backport of the CFS scheduler to 2.6.21, see > http://lkml.org/lkml/2007/11/19/127 > Hi, Simon:
I will try that after the thanksgiving holiday to find out whether the odd behavior will show up using 2.6.21 with back ported CFS.
>>>> Kernel 2.6.21 >>>> Number of Threads 2 4 6 8 >>>> SpinLock (Time micro second) 10.5618 10.58538 10.5915 10.643 >>>> (Overhead) 0.073 0.05746 0.102805 0.154563 >>>> Barrier (Time micro second) 11.020410 11.678125 11.9889 12.38002 >>>> (Overhead) 0.531660 1.1502 1.500112 1.891617 >>>> >>>> Each thread is bound to a particular core using pthread_setaffinity_np. >>>> >>>> Kernel 2.6.23.8 >>>> Number of Threads 2 4 6 8 >>>> SpinLock (Time micro second) 14.849915 17.117603 14.4496 10.5990 >>>> (Overhead) 4.345417 6.617207 3.949435 0.110985 >>>> Barrier (Time micro second) 19.462255 20.285117 16.19395 12.37662 >>>> (Overhead) 8.957755 9.784722 5.699590 1.869518 >>>>
> > > Simon Holm Thøgersen > > I just ran a simple test to prove that the problem may be related to load balance of the scheduler. I first started 6 processes using "taskset -c 2 donothing&; taskset -c 3 donothing&; ..., taskset -c 7 donothing". These 6 processes will run on core 2 to 7. Then I started my test program using two threads bound to core 0 and 1. Here is the result:
Two threads on Kernel 2.6.23.8: SpinLock (Time micro second) 10.558255 (Overhead) 0.068965 Barrier (Time micro second) 10.865520 (Overhead) 0.376230
Similarly, I started 4 donothing processes on core 4, 5, 6 and 7, and ran the test program. I have the following result:
Four threads on Kernel 2.6.23.8: SpinLock (Time micro second) 10.579413 (Overhead) 0.090023 Barrier (Time micro second) 11.363193 (Overhead) 0.873803
Finally, here is the result for 6 threads with two donothing processes running on core 6 and 7:
Six threads on Kernel 2.6.23.8: SpinLock (Time micro second) 10.590030 (Overhead) 0.100940 Barrier (Time micro second) 11.977548 (Overhead) 1.488458
Now the above results are very much similar to the results obtained for the kernel 2.6.21. I hope this helps you guys in some ways. Thank you.
-- ############################################################################# # Jie Chen # Scientific Computing Group # Thomas Jefferson National Accelerator Facility # Newport News, VA 23606 # # chen@jlab.org # (757)269-5046 (office) # (757)269-6248 (fax) ############################################################################# - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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