lkml.org 
[lkml]   [2007]   [Nov]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Possible bug from kernel 2.6.22 and above
    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.
    -
    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/

    \
     
     \ /
      Last update: 2007-11-22 21:25    [W:4.235 / U:0.156 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site