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    SubjectRe: NFS client latencies
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    Date
    On Tue, 2005-03-29 at 18:18 -0500, Trond Myklebust wrote:
    > ty den 29.03.2005 Klokka 18:04 (-0500) skreiv Lee Revell:
    > > I am seeing long latencies in the NFS client code. Attached is a ~1.9
    > > ms latency trace.
    >
    > What kind of workload are you using to produce these numbers?
    >

    Here is the other long latency I am seeing in the NFS client. I posted
    this before, but did not cc: the correct people.

    It looks like nfs_wait_on_requests is doing thousands of
    radix_tree_gang_lookups while holding some lock.

    Lee

    preemption latency trace v1.1.4 on 2.6.12-rc1-RT-V0.7.41-00
    --------------------------------------------------------------------
    latency: 3178 �s, #4095/14224, CPU#0 | (M:preempt VP:0, KP:1, SP:1 HP:1
    #P:1)
    -----------------
    | task: ksoftirqd/0-2 (uid:0 nice:-10 policy:0 rt_prio:0)
    -----------------

    _------=> CPU#
    / _-----=> irqs-off
    | / _----=> need-resched
    || / _---=> hardirq/softirq
    ||| / _--=> preempt-depth
    |||| /
    ||||| delay
    cmd pid ||||| time | caller
    \ / ||||| \ | /
    (T1/#0) <...> 32105 0 3 00000004 00000000 [0011939614227867]
    0.000ms (+4137027.445ms): <6500646c> (<61000000>)
    (T1/#2) <...> 32105 0 3 00000004 00000002 [0011939614228097]
    0.000ms (+0.000ms): __trace_start_sched_wakeup+0x9a/0xd0 <c013150a>
    (try_to_wake_up+0x94/0x140 <c0110474>)
    (T1/#3) <...> 32105 0 3 00000003 00000003 [0011939614228436]
    0.000ms (+0.000ms): preempt_schedule+0x11/0x80 <c02b57c1>
    (try_to_wake_up+0x94/0x140 <c0110474>)
    (T3/#4) <...>-32105 0dn.3 0�s : try_to_wake_up+0x11e/0x140
    <c01104fe> <<...>-2> (69 76):
    (T1/#5) <...> 32105 0 3 00000002 00000005 [0011939614228942]
    0.000ms (+0.000ms): preempt_schedule+0x11/0x80 <c02b57c1>
    (try_to_wake_up+0xf8/0x140 <c01104d8>)
    (T1/#6) <...> 32105 0 3 00000002 00000006 [0011939614229130]
    0.000ms (+0.000ms): wake_up_process+0x35/0x40 <c0110555> (do_softirq
    +0x3f/0x50 <c011b05f>)
    (T6/#7) <...>-32105 0dn.1 1�s < (1)
    (T1/#8) <...> 32105 0 2 00000001 00000008 [0011939614229782]
    0.001ms (+0.000ms): radix_tree_gang_lookup+0xe/0x70 <c01e05ee>
    (nfs_wait_on_requests+0x6d/0x110 <c01c744d>)
    (T1/#9) <...> 32105 0 2 00000001 00000009 [0011939614229985]
    0.001ms (+0.000ms): __lookup+0xe/0xd0 <c01e051e> (radix_tree_gang_lookup
    +0x52/0x70 <c01e0632>)
    (T1/#10) <...> 32105 0 2 00000001 0000000a [0011939614230480]
    0.001ms (+0.000ms): radix_tree_gang_lookup+0xe/0x70 <c01e05ee>
    (nfs_wait_on_requests+0x6d/0x110 <c01c744d>)
    (T1/#11) <...> 32105 0 2 00000001 0000000b [0011939614230634]
    0.002ms (+0.000ms): __lookup+0xe/0xd0 <c01e051e> (radix_tree_gang_lookup
    +0x52/0x70 <c01e0632>)
    (T1/#12) <...> 32105 0 2 00000001 0000000c [0011939614230889]
    0.002ms (+0.000ms): radix_tree_gang_lookup+0xe/0x70 <c01e05ee>
    (nfs_wait_on_requests+0x6d/0x110 <c01c744d>)
    (T1/#13) <...> 32105 0 2 00000001 0000000d [0011939614231034]
    0.002ms (+0.000ms): __lookup+0xe/0xd0 <c01e051e> (radix_tree_gang_lookup
    +0x52/0x70 <c01e0632>)
    (T1/#14) <...> 32105 0 2 00000001 0000000e [0011939614231302]
    0.002ms (+0.000ms): radix_tree_gang_lookup+0xe/0x70 <c01e05ee>
    (nfs_wait_on_requests+0x6d/0x110 <c01c744d>)
    (T1/#15) <...> 32105 0 2 00000001 0000000f [0011939614231419]
    0.002ms (+0.000ms): __lookup+0xe/0xd0 <c01e051e> (radix_tree_gang_lookup
    +0x52/0x70 <c01e0632>)

    (last two lines just repeat)


    > Cheers,
    > Trond

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