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
#
# [email protected]
# (757)269-5046 (office)
# (757)269-6248 (fax)
#############################################################################
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