Matthew Wilcox and I were talking about spin-then-sleep semaphores the
last few days and I asked for a workload that uses a lot of semaphores
to cause a lot of schedule()s. I think I found one:
Here's a quick readprofile during a Specweb99 run. Note, this is a
completely "stupid" run. I have done _no_ tuning and applied _no_
patches to the stock 2.5.25. I'm using Apache 2.0, without Tux, but
with mod_specweb99 on an 8xPIII-700-1MB with 18GB of RAM (no you can't
have one). I probably shouldn't state how many connections I'm
attempting, but it's more than 1 and less than a million :)
1 copy_files 0.0014
1 do_fork 0.0005
1 dup_task_struct 0.0089
1 error_code 0.0167
1 flush_tlb_all 0.0078
1 flush_tlb_page 0.0089
1 __global_cli 0.0027
1 init_bh 0.0312
1 sys_getgid 0.0625
1 sys_ipc 0.0016
2 alloc_ldt 0.0054
2 copy_mm 0.0026
2 init_new_context 0.0074
2 ksoftirqd 0.0074
2 sys_rt_sigprocmask 0.0037
2 tqueue_bh 0.0625
2 try_to_wake_up 0.0039
3 cpu_idle 0.0268
3 sys_getpid 0.1875
6 __write_lock_failed 0.1875
7 pgd_alloc 0.0312
7 resume_userspace 0.4375
8 sys_getppid 0.1667
10 ret_from_intr 0.6250
10 smp_call_function 0.0284
11 __wake_up_sync 0.0625
12 __run_task_queue 0.1071
12 __up_wakeup 1.0000
13 pte_alloc_one 0.0739
13 will_become_orphaned_pgrp 0.1016
14 add_wait_queue 0.2917
14 __down_failed_interruptible 1.1667
15 __up 0.4688
18 __down_failed 1.5000
18 .text.lock.fault 0.1295
21 __tasklet_schedule 0.1875
22 exit_notify 0.0275
28 session_of_pgrp 0.2188
31 syscall_call 2.8182
32 __down_interruptible 0.1250
38 sys_time 0.4750
45 del_timer 0.5625
50 bh_action 0.3906
57 tasklet_hi_action 0.2969
65 sys_wait4 0.0616
88 sys_mmap2 0.5500
94 tasklet_action 0.4896
127 .text.lock.sched 0.2433
135 syscall_exit 12.2727
141 schedule_timeout 0.8812
204 sys_gettimeofday 1.2750
350 __down 1.6827
399 flush_tlb_mm 3.5625
507 remove_wait_queue 7.9219
558 add_wait_queue_exclusive 11.6250
562 do_page_fault 0.4166
672 add_timer 3.0000
777 del_timer_sync 4.8563
850 handle_IRQ_event 5.9028
902 timer_bh 1.2812
1489 system_call 33.8409
1574 default_idle 24.5938
2594 do_softirq 12.4712
5222 do_gettimeofday 36.2639
5767 __wake_up 51.4911
5822 mod_timer 24.2583
5850 schedule 6.3039
35291 total 0.2881
Notice the large number of calls to down(). We're hitting a lot of
semaphores which are probably causing a big chunk of the scheduling.
I also Matthew's nemisis, the bottom half.
we (IBM LTC) have fixes for this: (John Stultz)
5222 do_gettimeofday 36.2639
and some which help this too: (akpm's smptimers and some smart
updating logic)
5822 mod_timer 24.2583
-- Dave Hansen haveblue@us.ibm.com- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Mon Jul 15 2002 - 22:00:14 EST