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    SubjectRe: Busy-wait delay in qmail 1.03 after upgrading to Linux 2.6
    [Andrew Morton]

    > OK, that's inconclusive. Could you do a few runs, or leave it a day or
    > two, wait until the problem is really prominent and see if you can gather a
    > clearer profile? The profiling overhead is negligible when profiling is
    > enabled but not in use, so there is no need to reboot.

    I tried running the test over and over, and after around 20 times,
    it suddenly jumped from 0.3 seconds to 1.6 again. Results follow:

    strace:

    678 01:04:16.722816 write(5, "\0", 1) = 1 <1.635007>

    time:

    real 0m1.666s
    user 0m0.008s
    sys 0m0.005s

    prof.time:

    c0139ea0 buffered_rmqueue 9 0.0256
    c0141e10 page_address 9 0.0469
    c0151a70 get_unused_fd 9 0.0216
    c0161830 open_namei 9 0.0089
    c01f8500 bin_search_in_dir_item 9 0.0511
    c0144040 do_anonymous_page 10 0.0189
    c0146300 find_vma 10 0.1042
    c013d650 kmem_cache_free 11 0.1375
    c0145ab0 do_mmap_pgoff 11 0.0061
    c0153640 __fput 11 0.0382
    c0161180 path_lookup 11 0.0362
    c01654f0 __pollwait 11 0.0529
    c022bec0 memcpy 11 0.1146
    c011aad0 add_wait_queue 12 0.1250
    c0151860 dentry_open 12 0.0227
    c01539b0 __constant_c_and_count_memset 12 0.0833
    c0151d50 filp_close 13 0.0903
    c01f85b0 search_by_entry_key 13 0.0262
    c01457c0 vma_merge 14 0.0186
    c02112a0 is_tree_node 14 0.1250
    c0142a20 zap_pte_range 15 0.0347
    c022c650 __copy_from_user_ll 15 0.0852
    c015f640 pipe_poll 16 0.1250
    c01655c0 max_select_fd 16 0.0714
    c0117440 do_page_fault 17 0.0131
    c0106d30 default_idle 19 0.3958
    c013d6a0 kfree 20 0.1786
    c0153760 fget 21 0.3281
    c01606a0 link_path_walk 21 0.0091
    c022c5d0 __copy_to_user_ll 22 0.1719
    c0211030 is_leaf 23 0.0496
    c016aaa0 __d_lookup 28 0.0833
    c0203d70 reiserfs_readdir 28 0.0184
    c0155230 __find_get_block 36 0.1607
    c01656a0 do_select 47 0.0653
    c01659a0 sys_select 50 0.0391
    c0211310 search_by_key 90 0.0247
    c0109174 system_call 107 2.4318
    c022c0b0 fast_clear_page 119 1.2396
    00000000 total 1251 0.0005

    --
    Haakon
    -
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