scheduling problem test13-pre7

scheduling problem test13-pre7

[Mike Galbraith]

Hi,

While running iozone, I notice severe stalls of vmstat output
despite vmstat running SCHED_RR and mlockall().

With IKD, I ran a million line ktrace of such a stall, and find
no occurance of vmstat's pid.  (trace covers a ~full second of
kernel time)  The only user process which was scheduled during
this second was iozone itself (p262).  I have seen such stalls
last for ~5 seconds.

%TOT_TIME    TOT_USECS  AVG/CALL NCALLS KADDR    FUNCTION    PID
  0.0002%         2.15      2.15      1 c01077db __switch_to p4
  0.0025%        24.18      2.69      9 c01077db __switch_to p262
  0.0043%        41.91      0.86     49 c01077db __switch_to p0
  0.0049%        47.54      2.97     16 c01077db __switch_to p3
  0.0107%       102.83      1.80     57 c01077db __switch_to p6

Tail end of profile of this trace by pid:

%TOT_TIME    TOT_USECS  AVG/CALL NCALLS KADDR    FUNCTION          PID
  0.2485%      2394.91      1.22   1964 c0108fea ret_from_sys_call p262
  0.2496%      2405.70      0.61   3925 c0134f8b get_hash_table p262
  0.2555%      2462.40      0.31   7854 c0135052 buffer_insert_inode_queue p262
  0.2731%      2632.40      0.65   4029 c01a9bc7 ide_do_request p6
  0.3339%      3218.32      0.85   3788 c012bdd0 kmem_cache_alloc p262
  0.3899%      3757.91      0.18  21110 c012f1ee nr_free_pages p262
  0.4086%      3937.88      0.50   7848 c013573f getblk p262
  0.4385%      4225.65      0.32  13255 c011612a wake_up_process p262
  0.5245%      5055.25      0.24  21110 c012f23a nr_inactive_clean_pages p262
  0.5468%      5269.94      9.38    562 c012d017 swap_out p4
  0.7403%      7134.44      1.76   4046 c018a907 elevator_linus_merge p6
  2.8165%     27144.72      0.54  50589 c0137527 try_to_free_buffers p4
  3.1803%     30650.25     43.05    712 c0111caa apm_bios_call_simple p3
  3.8435%     37041.89      0.20 185504 c012cbf7 try_to_swap_out p4
  5.0470%     48641.41      0.95  51157 c012f179 __free_pages p4
  9.8731%     95152.96      0.54 177443 c0137527 try_to_free_buffers p6
 10.7010%    103132.39     26.28   3925 c020bb80 __generic_copy_from_user p262
 17.5982%    169604.69      0.94 180429 c012f179 __free_pages p6
 33.8960%    326677.23   2916.76    112 c0107171 default_idle p0
1048352 entries;    963762.98 total usecs.

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Re: scheduling problem test13-pre7

[Matti Aarnio]

On Sun, Dec 31, 2000 at 10:42:26AM +0100, Mike Galbraith wrote:
> Hi,
> 
> While running iozone, I notice severe stalls of vmstat output
> despite vmstat running SCHED_RR and mlockall().

   Lets eliminate the obvious:

   - Are you running with IDE disk ?
   - Does   hdparm  /dev/hda(whatever)    report:

	/dev/hda:
	 unmaskirq    =  0 (off)
	 using_dma    =  0 (off)

   The IKD uses local interrupts, so this isn't necessarily true...

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Re: scheduling problem test13-pre7

[Mike Galbraith]

On Sun, 31 Dec 2000, Matti Aarnio wrote:

> On Sun, Dec 31, 2000 at 10:42:26AM +0100, Mike Galbraith wrote:
> > Hi,
> > 
> > While running iozone, I notice severe stalls of vmstat output
> > despite vmstat running SCHED_RR and mlockall().
> 
>    Lets eliminate the obvious:
> 
>    - Are you running with IDE disk ?

Yes.

>    - Does   hdparm  /dev/hda(whatever)    report:
> 
> 	/dev/hda:
> 	 unmaskirq    =  0 (off)
> 	 using_dma    =  0 (off)

No.

/dev/hda:
 multcount    =  0 (off)
 I/O support  =  1 (32-bit)
 unmaskirq    =  1 (on)
 using_dma    =  1 (on)
 keepsettings =  1 (on)
 nowerr       =  0 (off)
 readonly     =  0 (off)
 readahead    =  8 (on)
 geometry     = 2482/255/63, sectors = 39876480, start = 0

> 
>    The IKD uses local interrupts, so this isn't necessarily true...

I just did a (mondo) trace covering 8 seconds of kernel time, and
vmstat ran twice.  (Those two times were before I noticed the stall
and started counting down toward 'poke the freeze-frame button')

	-Mike

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