Re: [RFC, PATCH] cond_resched() added to close_files()

[Lee Revell]

On Fri, 2006-05-12 at 12:20 +0200, Ingo Molnar wrote:
> * Andrew Morton <akpm@xxxxxxxx> wrote:
> 
> > Makes my machine hang early during the startup of init.
> > 
> > The last process to pass through close_file() is `hostname', presuably 
> > parented by init.  `hostname' exits then everything stops.  init is 
> > left sleeping in select().
> > 
> > All very strange.
> 
> weird. This really shouldnt cause a hang - i think there must be a bug 
> hiding elsewhere, this cond_resched() ought to be fine.
> 

Ingo,

Would this be the latency it fixes? (seen with 2.6.16):

preemption latency trace v1.1.5 on 2.6.16
--------------------------------------------------------------------
 latency: 9313 us, #12766/12766, CPU#0 | (M:rt VP:0, KP:0, SP:0 HP:0)
    -----------------
    | task: jackd-26580 (uid:1000 nice:0 policy:1 rt_prio:80)
    -----------------

                 _------=> CPU#            
                / _-----=> irqs-off        
               | / _----=> need-resched    
               || / _---=> hardirq/softirq 
               ||| / _--=> preempt-depth   
               |||| /                      
               |||||     delay             
   cmd     pid ||||| time  |   caller      
      \   /    |||||   \   |   /           
ldconfig-26779 0d.h5    0us : __trace_start_sched_wakeup
(try_to_wake_up)
ldconfig-26779 0d.h5    1us : __trace_start_sched_wakeup <<...>-26580>
(13 0)
ldconfig-26779 0d.h.    2us : kill_fasync (snd_pcm_period_elapsed)
ldconfig-26779 0d.h.    3us : snd_emu10k1_voice_intr_ack
(snd_emu10k1_interrupt)
ldconfig-26779 0d.h.    5us+: snd_emu10k1_ptr_read
(snd_emu10k1_interrupt)
ldconfig-26779 0d.h.    8us+: snd_emu10k1_ptr_read
(snd_emu10k1_interrupt)
ldconfig-26779 0d.h1   12us : note_interrupt (__do_IRQ)
ldconfig-26779 0d.h1   13us : end_8259A_irq (__do_IRQ)
ldconfig-26779 0d.h1   13us : enable_8259A_irq (end_8259A_irq)
ldconfig-26779 0dnh2   15us : irq_exit (do_IRQ)
ldconfig-26779 0dn.2   16us < (2097760)
ldconfig-26779 0dn.2   17us : preempt_schedule (find_get_page)
ldconfig-26779 0dn.2   18us : put_page (free_file)
ldconfig-26779 0dn.2   18us : free_file (unmap_vmas)
ldconfig-26779 0dn.2   19us : find_get_page (free_file)
ldconfig-26779 0dn.3   20us : radix_tree_lookup (find_get_page)
ldconfig-26779 0dn.2   20us : preempt_schedule (find_get_page)
ldconfig-26779 0dn.2   21us : put_page (free_file)
ldconfig-26779 0dn.2   22us : free_file (unmap_vmas)
ldconfig-26779 0dn.2   22us : find_get_page (free_file)
ldconfig-26779 0dn.3   23us : radix_tree_lookup (find_get_page)
ldconfig-26779 0dn.2   24us : preempt_schedule (find_get_page)
ldconfig-26779 0dn.2   24us : put_page (free_file)
ldconfig-26779 0dn.2   25us : free_file (unmap_vmas)
ldconfig-26779 0dn.2   26us : find_get_page (free_file)
ldconfig-26779 0dn.3   26us : radix_tree_lookup (find_get_page)
ldconfig-26779 0dn.2   27us : preempt_schedule (find_get_page)

(...)

ldconfig-26779 0dn.2 9256us : put_page (free_file)
ldconfig-26779 0dn.2 9256us : free_file (unmap_vmas)
ldconfig-26779 0dn.2 9257us : find_get_page (free_file)
ldconfig-26779 0dn.3 9258us : radix_tree_lookup (find_get_page)
ldconfig-26779 0dn.2 9259us : preempt_schedule (find_get_page)
ldconfig-26779 0dn.2 9259us : put_page (free_file)
ldconfig-26779 0dn.2 9260us : free_file (unmap_vmas)
ldconfig-26779 0dn.2 9261us : find_get_page (free_file)
ldconfig-26779 0dn.3 9261us : radix_tree_lookup (find_get_page)
ldconfig-26779 0dn.2 9262us : preempt_schedule (find_get_page)
ldconfig-26779 0dn.2 9263us : put_page (free_file)
ldconfig-26779 0dn.1 9263us+: preempt_schedule (unmap_vmas)
ldconfig-26779 0dn.1 9266us : free_pgtables (unmap_region)
ldconfig-26779 0dn.1 9267us : anon_vma_unlink (free_pgtables)
ldconfig-26779 0dn.1 9269us : unlink_file_vma (free_pgtables)
ldconfig-26779 0dn.2 9269us : __remove_shared_vm_struct
(unlink_file_vma)
ldconfig-26779 0dn.2 9270us : vma_prio_tree_remove
(__remove_shared_vm_struct)
ldconfig-26779 0dn.2 9271us : prio_tree_remove (vma_prio_tree_remove)
ldconfig-26779 0dn.1 9273us : preempt_schedule (unlink_file_vma)
ldconfig-26779 0dn.1 9274us : free_pgd_range (free_pgtables)
ldconfig-26779 0dn.1 9275us : free_page_and_swap_cache (free_pgd_range)
ldconfig-26779 0dn.1 9276us : put_page (free_page_and_swap_cache)
ldconfig-26779 0dn.1 9277us : __page_cache_release (put_page)
ldconfig-26779 0dn.1 9278us : preempt_schedule (__page_cache_release)
ldconfig-26779 0dn.1 9279us : free_hot_page (__page_cache_release)
ldconfig-26779 0dn.1 9279us : free_hot_cold_page (free_hot_page)
ldconfig-26779 0dn.2 9280us : __mod_page_state_offset
(free_hot_cold_page)
ldconfig-26779 0dn.1 9281us : preempt_schedule (free_hot_cold_page)
ldconfig-26779 0dn.1 9282us : mod_page_state_offset (free_pgd_range)
ldconfig-26779 0dn.1 9283us : free_page_and_swap_cache (free_pgd_range)
ldconfig-26779 0dn.1 9284us : put_page (free_page_and_swap_cache)
ldconfig-26779 0dn.1 9285us : __page_cache_release (put_page)
ldconfig-26779 0dn.1 9285us : preempt_schedule (__page_cache_release)
ldconfig-26779 0dn.1 9286us : free_hot_page (__page_cache_release)
ldconfig-26779 0dn.1 9287us : free_hot_cold_page (free_hot_page)
ldconfig-26779 0dn.2 9287us : __mod_page_state_offset
(free_hot_cold_page)
ldconfig-26779 0dn.1 9288us : preempt_schedule (free_hot_cold_page)
ldconfig-26779 0dn.1 9289us : mod_page_state_offset (free_pgd_range)
ldconfig-26779 0dn.1 9290us : free_page_and_swap_cache (free_pgd_range)
ldconfig-26779 0dn.1 9291us : put_page (free_page_and_swap_cache)
ldconfig-26779 0dn.1 9291us : __page_cache_release (put_page)
ldconfig-26779 0dn.1 9292us : preempt_schedule (__page_cache_release)
ldconfig-26779 0dn.1 9293us : free_hot_page (__page_cache_release)
ldconfig-26779 0dn.1 9293us : free_hot_cold_page (free_hot_page)
ldconfig-26779 0dn.2 9294us : __mod_page_state_offset
(free_hot_cold_page)
ldconfig-26779 0dn.1 9295us : preempt_schedule (free_hot_cold_page)
ldconfig-26779 0dn.1 9295us : mod_page_state_offset (free_pgd_range)
ldconfig-26779 0dn.. 9297us : preempt_schedule (unmap_region)
ldconfig-26779 0dn.. 9298us : schedule (preempt_schedule)
ldconfig-26779 0dn.. 9298us : profile_hit (schedule)
ldconfig-26779 0dn.1 9299us+: sched_clock (schedule)
   <...>-26580 0d..2 9306us+: __switch_to (schedule)
   <...>-26580 0d..2 9309us : schedule <ldconfig-26779> (76 13)
   <...>-26580 0d..1 9310us : trace_stop_sched_switched (schedule)
   <...>-26580 0d..2 9310us : trace_stop_sched_switched <<...>-26580>
(13 0)
   <...>-26580 0d..2 9312us : schedule (schedule)

Lee

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