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    SubjectRe: Poor UDP performance using 2.6.21-rc5-rt5
    Date
    I have a new data point to add to the confusion.

    The box I'm testing has 2 nics in it. The one I have been testing so far is:

    00:08.0 Bridge: nVidia Corporation MCP55 Ethernet (rev a3)

    The other NIC is an Intel 1gig fiber

    09:00.0 Ethernet controller: Intel Corporation 82571EB Gigabit Ethernet Controller (rev 06)

    The Intel controller did not work 2.6.20 but under 2.6.21-rc5-rt8 it does.

    Running the same netperf tests with the Intel NIC produces very different results for the RT case:


    setup Thruput CPU%
    Nvidia
    2.6.21-rc5 vanilla 935 29%
    netperf @51
    hardirq @50
    softirq @50

    Intel
    2.6.21-rc5 vanilla 933 30%
    netperf @51
    hardirq @50
    softirq @50

    ##################################################
    Nvidia
    2.6.21-rc5-rt8 938 65%
    netperf @51
    hardirq @50
    softirq @50

    Intel
    2.6.21-rc5-rt8 938 34%
    netperf @51
    hardirq @50
    softirq @50

    The Intel NIC seems to behave better under RT

    top for each NIC under test yields some interesting results:

    Nvidia 2.6.21-rc5-rt8:
    top - 11:03:46 up 1:23, 2 users, load average: 1.75, 1.31, 0.70
    Tasks: 167 total, 2 running, 165 sleeping, 0 stopped, 0 zombie
    Cpu(s): 0.8%us, 29.7%sy, 0.0%ni, 34.8%id, 0.0%wa, 22.1%hi, 10.6%si, 0.0%st
    Mem: 2035436k total, 618276k used, 1417160k free, 31744k buffers
    Swap: 3068372k total, 0k used, 3068372k free, 386060k cached

    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    4139 root -52 0 6440 636 480 S 60 0.0 0:19.14 netperf
    2706 root -51 -5 0 0 0 R 44 0.0 2:00.70 IRQ-8406
    19 root -51 0 0 0 0 S 21 0.0 0:38.50 softirq-net-tx/
    4012 eadi 16 0 229m 6852 5584 S 1 0.3 0:05.39 multiload-apple
    6 root -51 0 0 0 0 S 1 0.0 0:00.95 softirq-net-tx/
    3014 dbus 15 0 21352 896 548 S 1 0.0 0:00.04 dbus-daemon
    1 root 15 0 10308 668 552 S 0 0.0 0:00.74 init
    2 root RT 0 0 0 0 S 0 0.0 0:00.00 migration/0
    3 root RT 0 0 0 0 S 0 0.0 0:00.00 posix_cpu_timer
    4 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-high/0
    5 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-timer/0
    7 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-net-rx/
    8 root -51 0 0 0 0 S 0 0.0 0:00.01 softirq-block/0

    ########################
    Intel 2.6.21-rc5-rt8
    top - 11:10:27 up 3 min, 2 users, load average: 0.00, 0.00, 0.00
    Tasks: 167 total, 1 running, 166 sleeping, 0 stopped, 0 zombie
    Cpu(s): 0.5%us, 21.6%sy, 0.0%ni, 65.9%id, 0.0%wa, 3.0%hi, 9.0%si, 0.0%st
    Mem: 2035436k total, 618012k used, 1417424k free, 29972k buffers
    Swap: 3068372k total, 0k used, 3068372k free, 386084k cached

    PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
    3955 root -52 0 6436 636 480 S 43 0.0 0:19.74 netperf
    20 root -51 0 0 0 0 S 11 0.0 0:04.86 softirq-net-rx/
    7 root -51 0 0 0 0 S 7 0.0 0:03.28 softirq-net-rx/
    2370 root -51 -5 0 0 0 S 6 0.0 0:02.62 IRQ-8408
    3858 eadi 16 0 229m 6848 5584 S 1 0.3 0:01.45 multiload-apple
    3954 eadi 15 0 12712 1096 788 R 0 0.1 0:00.19 top
    1 root 15 0 10304 664 552 S 0 0.0 0:00.75 init
    2 root RT 0 0 0 0 S 0 0.0 0:00.00 migration/0
    3 root RT 0 0 0 0 S 0 0.0 0:00.00 posix_cpu_timer
    4 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-high/0
    5 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-timer/0
    6 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-net-tx/
    8 root -51 0 0 0 0 S 0 0.0 0:00.01 softirq-block/0
    9 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-tasklet
    10 root -51 0 0 0 0 S 0 0.0 0:00.00 softirq-sched/0
    ############################

    I think there is some kind of bad behavior happening in the Nvidia driver
    with respect to softirq-net-tx and IRQ-8406.

    Any thoughts? If you want I can post the oprofile from both test cases.

    -Dave

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