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    SubjectRe: ~5x greater CPU load for a networked application when using 2.6.15-rt15-smp vs. 2.6.12-1.1390_FC4
    Andrew Morton wrote:
    > Ingo Molnar <> wrote:
    >>To figure out the true overhead of both kernels, could you try the
    >> attached loop_print_thread.c code

    > <- better ;)


    I read the README for the "zc" tests. I wish Ingo can opine on which may be a
    better test. Also, i assume that I can run "zcs" and "zcc" on the same
    machine. I would do the tests with "send" instead of "sendfile".

    I also have some other test data. The graphical summary result can be viewed
    at this link:

    In these tests I used a single Intel Xeon 3GH dual processor machine with 4
    different kernels, all based on 2.6.14

    2.6.14 Uniprocessor kernel
    2.6.14-rt22 Uniprocessor kernel w/ RT patches
    2.6.14-smp SMP kernel
    2.6.14-rt22-smp SMP kernel w/ RT patches.

    The test is similar to "zcs", "zcc" tests. In my tests a client process opens
    a TCP connection to the server process (all on same machine) and sends to it
    10,000,000 messages of sizes 4 bytes, 8 bytes, 16 bytes, .... , 32Kbytes,
    64Kbytes. The server sends back a 1 byte reply. The client measures roundtrip
    latencies. The graphic shows mean roundtrip latencies. Since measuremnts are
    taken over so many samples I believe that the large differences in mean
    latencies capture the relative CPU consumption of various kernel. (This being
    loopback there are no NIC card issues or otherwise.) One notices a 3:1 ration
    here from uniprocessor, non-RT kernel to SMP-RT kernel. The RT kernel has
    nice real-time properties, and there is a lot of pressure in our systems to
    use the SMP hardware of the multicore machines, and in some cases we can even
    with with a 3x slowdown (since real applications do more than just I/O), but
    when I started to note 5x (or more) in my newer tests I thought I would at
    least post something.

    I suspect that "zcs"/"zcc" tests would pretty much show the same conclusions
    as this graphic.

    Gautam H. Thaker
    Distributed Processing Lab; Lockheed Martin Adv. Tech. Labs
    3 Executive Campus; Cherry Hill, NJ 08002
    856-792-9754, fax 856-792-9925 email:
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