(un)likely profiling....

From: Daniel J Blueman
Date: Sun Feb 22 2009 - 19:54:35 EST

A developer's desktop workload (NFS, GCC, UXA+compiz) and
likely/unlikely macro profiling shows some interesting results [1]
(line numbers against 2.6.29-rc5).

It's clear many are false-positives due to other kernel debug
mechanisms, some are due to IS_ERR() macro assumptions being used
along error paths and others are insignificant, but a quick check show
there are a few dubious/potentially mislabeled (~workload dependent?)
ones, eg filemap.c:grab_cache_page_write_begin,
nfs4xdr.c:decode_attr_*, timer.c:timer_stats_account_timer perhaps?

I guess the hot/cold path partitioning costs may have been considered
for important cases, making things less obvious on some too...

Daniel

--- [1]

# sort -nbk3 /sys/kernel/debug/tracing/profile_annotated_branch | tail -n60
correct incorrect % Function File Line
------- --------- - -------- ---- ----
8968248 5267043 36 __switch_to process_64.c 561
1815 1112 37 need_resched sched.h 2157
827587 491835 37 net_rx_action dev.c 2741
8912232 5323142 37 __switch_to process_64.c 641
8968128 5267012 37 __switch_to process_64.c 557
479719 318359 39 tcp_write_xmit tcp_output.c 1592
8830 5844 39 load_balance sched.c 3524
8592950 5973868 41 pick_next_task sched.c 4524
164982384 155024719 48 read_seqbegin seqlock.h 93
148893156 145236077 49 read_seqbegin seqlock.h 93
36 36 50 compound_head mm.h 289
746777 760049 50 copy_stack_frame trace_sysprof.c 45
245273 257959 51 copy_pte_range memory.c 617
14487 18674 56 unmap_mapping_range memory.c 2300
481759 984637 67 tcp_transmit_skb tcp_output.c 617
47846 111579 69 syscall_get_error syscall.h 51
132 311 70 inotify_find_update_watch inotify.c 726
177097 420276 70 grab_cache_page_write_begin filemap.c 2159
15541 39878 71 next_pidmap pid.c 194
4606 13746 74 pmd_alloc mm.h 930
56 164 74 ioremap_pte_range ioremap.c 22
11 34 75 grab_swap_token thrash.c 51
3506556 10728943 75 __switch_to process_64.c 591
38 127 76 clocksource_adjust timekeeping.c 453
2 8 80 usb_alloc_dev usb.c 376
1443919 7833307 84 page_mapping mm.h 647
69498 456086 86 timer_stats_account_timer timer.c 381
17420569 128401540 88 __slab_free slub.c 1665
239 2001 89 remap_pte_range memory.c 1577
20496 318913 93 fput_light file.h 29
23329 439767 94 queue_delayed_work_on workqueue.c 252
415199 7833291 94 mapping_unevictable pagemap.h 50
443 6992 94 sys_inotify_add_watch inotify_user.c 702
365 7138 95 fput_light file.h 29
1 32 96 __cancel_work_timer workqueue.c 560
2054 75222 97 tcp_mss_split_point tcp_output.c 1122
192744 88289793 99 debug_mutex_unlock mutex-debug.c 79
6345 8060994 99 pick_next_task_rt sched_rt.c 889
880 5982195 99 clocksource_adjust timekeeping.c 459
0 1 100 hpet_rtc_timer_reinit hpet.c 1066
0 1 100 srcu_notifier_chain_register notifier.c 427
0 1135 100 rt_mutex_slowlock rtmutex.c 648
0 117 100 verify_export_symbols module.c 1521
0 12 100 signal_pending sched.h 2135
0 12490918 100 sched_info_queued sched_stats.h 223
0 14235223 100 sched_info_switch sched_stats.h 270
0 145827757 100 slab_free slub.c 1728
0 145831331 100 __slab_free slub.c 1657
0 146192625 100 slab_alloc slub.c 1607
0 146199943 100 __slab_alloc slub.c 1529
0 15 100 signal_pending sched.h 2135
0 195578 100 __free_slab slub.c 1161
0 2 100 ehci_irq ehci-hcd.c 678
0 213591 100 new_slab slub.c 1138
0 21482 100 sched_move_task sched.c 8899
0 21482 100 sched_move_task sched.c 8909
0 22 100 blocking_notifier_chain_regist notifier.c 220
0 3473 100 IS_ERR err.h 34
0 372096 100 decode_attr_fs_locations nfs4xdr.c 2432
0 372097 100 decode_attr_mounted_on_fileid nfs4xdr.c 2320
0 4 100 clear_page_mlock internal.h 130
0 4 100 scan_async ehci-q.c 1123
0 6347 100 pre_schedule_rt sched_rt.c 1263
0 9595216 100 sched_info_dequeued sched_stats.h 178
--
Daniel J Blueman
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