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Date: Fri, 22 Jun 2012 15:53:05 -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 3:42 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: 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 Stall (one of many b/t insert and dispatch): 8,0 1 296851 4852.776942694 8216 U N [httpdmon] 1 8,0 1 0 4852.776945488 0 m N cfq select_queue: !cfqq 8,0 1 0 4852.776946885 0 m N cfq select_queue: cfq_choose_cfqg 8,0 1 0 4852.776948281 0 m N cfq select_queue: setting active queue to new_cfqq:NULL 8,0 1 0 4852.776950237 0 m N cfq8216 set_active wl_prio:0 wl_type:1 8,0 1 0 4852.776951634 0 m N cfq8216 del timer 8,0 1 0 4852.776952751 0 m N cfq8216 update idle time stats 8,0 1 0 4852.776954427 0 m N cfq8216 Idling on sync. st->count:1 8,0 1 0 4852.776957780 0 m N cfq8216 fifo= (null) 8,0 1 0 4852.776959456 0 m N cfq8216 dispatch_insert 8,0 1 0 4852.776961412 0 m N cfq8216 remove request 8,0 1 0 4852.776963647 0 m N cfq8216 dispatched a request 8,0 1 0 4852.776965043 0 m N cfq8216 activate rq, drv=1 8,0 1 296852 4852.776966161 8216 D R 13529455 + 8 ( 34642) [httpdmon] 8,0 1 0 4852.777044943 0 m N cfq8216 Idling on sync. st->count:1 8,0 1 0 4852.777046340 0 m N cfq8216 select_queue: dispatched and should_idle - keep_queue 8,0 0 440281 4852.777130150 7284 C R 13529455 + 8 ( 163989) [0] 8,0 0 0 4852.777145236 0 m N cfq8216 complete rqnoidle 0 8,0 0 0 4852.777147471 0 m N cfq8216 set_slice=100 8,0 0 0 4852.777149427 0 m N cfq8216 arm slice timer 8,0 0 0 4852.777151103 0 m N cfq8216 Idling on sync. st->count:1 8,0 0 0 4852.777153058 0 m N cfq8216 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 8,0 1 296750 4848.309956053 7646 Q R 33545872 + 8 [httpdmon] Dispatch: 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 In this case you see the schedule dispatch message so there were busy queues, but for whatever reason nothing gets run. Will keep digging. -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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