On Wed, Nov 21, 2007 at 09:58:10PM -0500, Jie Chen wrote:
> Simon Holm Th??gersen 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 Th??gersen
> >
> >
> 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.
Yes, this really does look like a scheduling regression. I've added
Ingo to the cc: list. Next time you should pick a more descriptive
subject line - we've got lots of email about possible bugs.
--
Mathematics is the supreme nostalgia of our time.
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