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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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