Message-ID: <CAKA=qza_s6zr+wZzfFTVPSzgPQAov=K63jf-SJOTDcrnDELY5w@mail.gmail.com>
Date:	Fri, 22 Jun 2012 15:57:48 -0500
From:	Josh Hunt <joshhunt00@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	tj@...nel.org
Subject: Re: multi-second application stall in open()

On Fri, Jun 22, 2012 at 3:53 PM, Josh Hunt <joshhunt00@...il.com> wrote:
> On Fri, Jun 22, 2012 at 3:42 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
>> On Fri, Jun 22, 2012 at 03:22:01PM -0500, Josh Hunt wrote:
>>
>> [..]
>>> It looks like my statement about busy_queues isn't entirely accurate.
>>> I'm seeing this later on in the trace:
>>
>> Yes it is being called some times. But it is interesting to see that in
>> the instance you pasted in last mail, we did not see "schedule_dispatch"
>> message.  Are you sure that other requests were queued at that point of
>> time and there were busy_queues? You can try printing cfqd->rq_queued
>> to verify that.
>>
>> Also put some message in cfq_select_queue() to see why it did not select
>> a new queue before the stall.
>>
>> Thanks
>> Vivek
>
> I think you may be correct that at those points in time there weren't
> any busy queues. I do know that there were requests waiting during
> this time:

Sorry. Please disregard the prev mail. Looks like I must have scrolled
my buffer while pasting in the traces... Here's what I meant to send:

Insert:
  8,0    1   296677  4847.796879805  6076  P   N [flush-8:0]
  8,0    1   296678  4847.796881202  6076  I   W 32800441 + 8 (
2794) [flush-8:0]
  8,0    1        0  4847.796883157     0  m   N cfq5917 insert_request
  8,0    1   296679  4847.796884834  6076  U   N [flush-8:0] 1
  8,0    1   296680  4847.796901037  6076  A   R 32499249 + 8 <- (8,3) 11534424
  8,0    1   296681  4847.796902154  6076  Q   R 32499249 + 8 [flush-8:0]
  8,0    1   296682  4847.796904389  6076  G   R 32499249 + 8 [flush-8:0]
  8,0    1   296683  4847.796906066  6076  I   R 32499249 + 8 (
1677) [flush-8:0]
  8,0    1        0  4847.796907462     0  m   N cfq6076 insert_request
  8,0    1        0  4847.796908859     0  m   N cfq6076 add_to_rr


Stall:
  8,0    1        0  4847.816870313     0  m   N cfq7646 insert_request
  8,0    1        0  4847.816873665     0  m   N cfq7646 del timer
  8,0    1        0  4847.816874783     0  m   N cfq7646 update idle time stats
  8,0    1        0  4847.816876738     0  m   N cfq7646 select_queue:
active requests/not expired - keep_queue
  8,0    1        0  4847.816878414     0  m   N cfq7646 Idling on
sync. st->count:1
  8,0    1        0  4847.816879811     0  m   N cfq7646 dispatch_insert
  8,0    1        0  4847.816882046     0  m   N cfq7646 remove request
  8,0    1        0  4847.816884002     0  m   N cfq7646 dispatched a request
  8,0    1        0  4847.816885399     0  m   N cfq7646 activate rq, drv=1
  8,0    1   296748  4847.816887075  7646  D   R 32499241 + 8 (
20115) [httpdmon]
  8,0    1        0  4847.816945463     0  m   N cfq7646 Idling on
sync. st->count:1
  8,0    1        0  4847.816946580     0  m   N cfq7646 select_queue:
dispatched and should_idle - keep_queue
  8,0    1        0  4847.816948536     0  m   N cfq7646 Idling on
sync. st->count:1
  8,0    1        0  4847.816949653     0  m   N cfq7646 select_queue:
dispatched and should_idle - keep_queue
  8,0    0   440261  4847.817104144  7284  C   R 32499241 + 8 (  217069) [0]
  8,0    0        0  4847.817110290     0  m   N cfq7646 complete rqnoidle 0
  8,0    0        0  4847.817112525     0  m   N cfq7646 arm slice timer
  8,0    0        0  4847.817113922     0  m   N cfq7646 Idling on
sync. st->count:1
  8,0    0        0  4847.817115878     0  m   N cfq7646 arm_idle: 8
group_idle: 0
  8,0    0        0  4847.817116995     0  m   N cfq schedule dispatch
  8,0    0        0  4847.817120068     0  m   N cfq7646 select_queue:
timer_pending - keep_queue
  8,0    0        0  4847.824613293     0  m   N cfq idle timer fired
  8,0    0        0  4847.824616366     0  m   N cfq7646
idle_slice_timer: active queue
  8,0    0        0  4847.824617763     0  m   N cfq7646
idle_slice_timer: clear_cfqq_deep
  8,0    0        0  4847.824619439     0  m   N cfq7646 slice expired t=0
  8,0    0        0  4847.824621395     0  m   N cfq7646 del timer
  8,0    0        0  4847.824622792     0  m   N cfq7646 update idle time stats
  8,0    0        0  4847.824625865     0  m   N cfq7646 sl_used=12
disp=3 charge=12 iops=0 sect=24
  8,0    0        0  4847.824627262     0  m   N cfq7646 slice_expired
del cfqq from rr
  8,0    0        0  4847.824628379     0  m   N cfq7646 del_from_rr
  8,0    0        0  4847.824629776     0  m   N cfq7646 slice_expired
resort_rr_list
  8,0    0        0  4847.824631452     0  m   N cfq7646 slice_expired
setting active_queue to NULL
  8,0    0        0  4847.824632849     0  m   N cfq7646 slice_expired
setting active_cic to NULL
  8,0    0        0  4847.824634246     0  m   N cfq schedule dispatch
  8,0    1   296749  4848.309940967  7646  A   R 33545872 + 8 <- (8,4) 2152

Dispatch:
  8,0    0        0  4857.832309642     0  m   N cfq5917 dispatched a request
  8,0    0        0  4857.832310760     0  m   N cfq5917 activate rq, drv=2
  8,0    0   440336  4857.832312157  7284  D   W 32800441 + 8
(10035430955) [testd]
  8,0    0   440337  4857.832447371  7284  C   W 2076271 + 8 (  687247) [0]
  8,0    0        0  4857.832457987     0  m   N cfq5917 complete rqnoidle 0

-- 
Josh
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