Scenario: Dell Latitude D820 laptop, Core2 Duo T7200 2.0Gz CPU, 64-bit kernel.
System ran fine on rc5-mmotm0829. When I built -mmotm0913, I changed the
CONFIG_FTRACE from 'n' to 'y'. The resulting kernel chews a *lot* of
system-mode time - even running 'xmms' (which on the older kernel only took
4-5% total CPU) was showing 20-25% system time. This morning, it was hitting
up to 95% system time while downloading my e-mail, a fetchmail/sendmail/procmail
pipeline. I ran some oprofile numbers (60 seconds worth of data per run):
Running xmms last night, 20-25% system CPU:
samples % symbol name
9712 22.0677 read_hpet
7003 15.9123 ftrace_caller
3931 8.9321 ftrace_call
2763 6.2781 native_read_tsc
1678 3.8128 hpet_next_event
1420 3.2265 tg_shares_up
610 1.3860 get_parent_ip
560 1.2724 test_ti_thread_flag
507 1.1520 native_sched_clock
479 1.0884 sched_clock_cpu
459 1.0429 __switch_to
428 0.9725 in_lock_functions
349 0.7930 getnstimeofday
Two runs from this morning, up to 80-95% system CPU:
samples % symbol name
11206 26.5068 ftrace_caller
8624 20.3993 ftrace_call
6252 14.7885 read_hpet
1746 4.1300 native_read_tsc
869 2.0555 tg_shares_up
696 1.6463 get_parent_ip
628 1.4855 hpet_next_event
599 1.4169 test_ti_thread_flag
441 1.0431 in_lock_functions
436 1.0313 __might_sleep
412 0.9745 flush_tlb_page
276 0.6529 system_call
samples % symbol name
16008 31.5131 ftrace_caller
12858 25.3120 ftrace_call
6174 12.1540 read_hpet
1212 2.3859 native_read_tsc
755 1.4863 get_parent_ip
731 1.4390 tg_shares_up
626 1.2323 __might_sleep
626 1.2323 test_ti_thread_flag
526 1.0355 in_lock_functions
479 0.9430 flush_tlb_page
353 0.6949 __phys_addr
314 0.6181 system_call
Roughly 2/3 of my total CPU capacity is getting sucked down ...
