bug in elevator/cfq regarding start

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* bug in elevator/cfq regarding start_time?
@ 2009-10-04 20:54 Corrado Zoccolo
  2009-10-04 20:59 ` Jens Axboe
  0 siblings, 1 reply; 7+ messages in thread
From: Corrado Zoccolo @ 2009-10-04 20:54 UTC (permalink / raw)
  To: Jens Axboe, Linux-Kernel

Hi Jens,
I found that the start_time is not monotonic in the cfqq fifo_list.
The problem seems to be that:
* attempt_merge overrides one of the start_time:
        if (time_after(req->start_time, next->start_time))
                req->start_time = next->start_time;
* then it calls elv_merge_requests, that in turn invokes cfq's
elevator_merge_req_fn, i.e. cfq_merged_requests
* cfq_merged_requests checks start_times to decide whether requests
need to be repositioned
        if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
            time_before(next->start_time, rq->start_time))
                list_move(&rq->queuelist, &next->queuelist);

Other I/O schedulers are not affected, since none of them uses
start_time explicitly, but they have a copy in one of the private
fields.

Corrado

-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@gmail.com
PhD - Department of Computer Science - University of Pisa, Italy
--------------------------------------------------------------------------

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: bug in elevator/cfq regarding start_time?
  2009-10-04 20:54 bug in elevator/cfq regarding start_time? Corrado Zoccolo
@ 2009-10-04 20:59 ` Jens Axboe
  2009-10-05 15:08   ` Corrado Zoccolo
  0 siblings, 1 reply; 7+ messages in thread
From: Jens Axboe @ 2009-10-04 20:59 UTC (permalink / raw)
  To: Corrado Zoccolo; +Cc: Linux-Kernel

On Sun, Oct 04 2009, Corrado Zoccolo wrote:
> Hi Jens,
> I found that the start_time is not monotonic in the cfqq fifo_list.
> The problem seems to be that:
> * attempt_merge overrides one of the start_time:
>         if (time_after(req->start_time, next->start_time))
>                 req->start_time = next->start_time;
> * then it calls elv_merge_requests, that in turn invokes cfq's
> elevator_merge_req_fn, i.e. cfq_merged_requests
> * cfq_merged_requests checks start_times to decide whether requests
> need to be repositioned
>         if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
>             time_before(next->start_time, rq->start_time))
>                 list_move(&rq->queuelist, &next->queuelist);
> 
> Other I/O schedulers are not affected, since none of them uses
> start_time explicitly, but they have a copy in one of the private
> fields.

Good spotting! So we can either add the same copy in cfq, or we can just
move the ->start_time check and assignment in attempt_merge() to post
the elv_merge_requests() call. I think the latter would work fine, but
I'll check and fix tomorrow.

-- 
Jens Axboe


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: bug in elevator/cfq regarding start_time?
  2009-10-04 20:59 ` Jens Axboe
@ 2009-10-05 15:08   ` Corrado Zoccolo
  2009-10-05 20:26     ` Corrado Zoccolo
  0 siblings, 1 reply; 7+ messages in thread
From: Corrado Zoccolo @ 2009-10-05 15:08 UTC (permalink / raw)
  To: Jens Axboe; +Cc: Linux-Kernel

On Sun, Oct 4, 2009 at 10:59 PM, Jens Axboe <jens.axboe@oracle.com> wrote:
> Good spotting! So we can either add the same copy in cfq, or we can just
> move the ->start_time check and assignment in attempt_merge() to post
> the elv_merge_requests() call. I think the latter would work fine, but
> I'll check and fix tomorrow.

I think there is still something buggy regarding those timestamps.
I added the following code:
               struct request *rq = rq_entry_fifo(cfqq->fifo.next);
                rb_key = jiffies;
                printk(KERN_INFO "Queue %p added at %lu with
start_time %lu, fifo_time %lu\n", cfqq, rb_key, rq->start_time,
rq_fifo_time(rq));
in the (!add_front) path of cfq_service_tree_add, and I get the puzzling:

[ 2892.252866] io scheduler cfq registered
[ 2900.785179] Queue f36a2700 added at 2600784 with start_time 0, fifo_time 0
[ 2900.785754] Queue f36a2dc0 added at 2600785 with start_time 0, fifo_time 0
[ 2900.802975] Queue f36a2700 added at 2600802 with start_time 0,
fifo_time 2600902
[ 2900.808695] Queue f36a2700 added at 2600808 with start_time 0,
fifo_time 2600902
[ 2900.813437] Queue f36a2700 added at 2600813 with start_time 0,
fifo_time 2600902
[ 2900.824576] Queue f36a2700 added at 2600824 with start_time 0,
fifo_time 2600902
[ 2900.835112] Queue f36a2694 added at 2600835 with start_time 0, fifo_time 0
[ 2900.836416] Queue f36a2700 added at 2600836 with start_time 0,
fifo_time 2600902
[ 2900.846350] Queue f36a2700 added at 2600846 with start_time 0,
fifo_time 2600902
[ 2900.856558] Queue f36a2700 added at 2600856 with start_time 0,
fifo_time 2600902
[ 2900.860327] Queue f36a2700 added at 2600860 with start_time 0,
fifo_time 2600902
[ 2900.868702] Queue f36a2700 added at 2600868 with start_time 0,
fifo_time 2600902
[ 2900.875067] Queue f36a2700 added at 2600875 with start_time 0,
fifo_time 2600902
[ 2900.887291] Queue f36a2700 added at 2600887 with start_time 0,
fifo_time 2600902
[ 2900.893159] Queue f36a2700 added at 2600893 with start_time 0,
fifo_time 2600902
[ 2900.899166] Queue f36a2700 added at 2600899 with start_time 0,
fifo_time 2600902
[ 2900.909187] Queue f36a2700 added at 2600909 with start_time 0,
fifo_time 2600902
[ 2900.918176] Queue f36a2dc0 added at 2600918 with start_time 0,
fifo_time 2601018
[ 2900.931307] Queue f36a2dc0 added at 2600931 with start_time 0,
fifo_time 2601018
[ 2900.947928] Queue f36a2dc0 added at 2600947 with start_time 0,
fifo_time 2601018
[ 2900.958411] Queue f36a2dc0 added at 2600958 with start_time 0,
fifo_time 2601018
[ 2900.972069] Queue f36a2694 added at 2600972 with start_time 1,
fifo_time 2601071
[ 2900.972091] Queue f36a2694 added at 2600972 with start_time 1,
fifo_time 2601071
[ 2900.972131] Queue f36a2694 added at 2600972 with start_time 1,
fifo_time 2601071
[ 2901.072721] Queue f36a2694 added at 2601072 with start_time
2601006, fifo_time 2601131
[ 2901.088532] Queue f36a2dc0 added at 2601088 with start_time 0,
fifo_time 2601188
[ 2901.093024] Queue f36a2dc0 added at 2601092 with start_time 0,
fifo_time 2601188
[ 2901.102174] Queue f36a2dc0 added at 2601102 with start_time 0,
fifo_time 2601188
[ 2901.108286] Queue f36a2dc0 added at 2601108 with start_time 0,
fifo_time 2601188
[ 2901.114145] Queue f36a2dc0 added at 2601114 with start_time 0,
fifo_time 2601188
[ 2901.126528] Queue f36a2dc0 added at 2601126 with start_time 0,
fifo_time 2601188
[ 2901.138521] Queue f36a2dc0 added at 2601138 with start_time 0,
fifo_time 2601188
[ 2901.145924] Queue f36a2dc0 added at 2601145 with start_time 0,
fifo_time 2601188
[ 2901.156286] Queue f36a2dc0 added at 2601156 with start_time 0,
fifo_time 2601188
[ 2901.158932] Queue f36a2dc0 added at 2601158 with start_time 0,
fifo_time 2601188
[ 2901.170278] Queue f36a2dc0 added at 2601170 with start_time 0,
fifo_time 2601188
[ 2901.178530] Queue f36a2dc0 added at 2601178 with start_time 0,
fifo_time 2601188
[ 2901.188418] Queue f36a2dc0 added at 2601188 with start_time 0,
fifo_time 2601188
[ 2901.201399] Queue f36a2700 added at 2601201 with start_time 0,
fifo_time 2601301
[ 2901.211661] Queue f36a2700 added at 2601211 with start_time 0,
fifo_time 2601301
[ 2901.221408] Queue f36a2700 added at 2601221 with start_time 0,
fifo_time 2601301
[ 2901.228884] Queue f36a2700 added at 2601228 with start_time 0,
fifo_time 2601301
[ 2901.240536] Queue f36a2700 added at 2601240 with start_time 0,
fifo_time 2601301
[ 2901.248675] Queue f36a2700 added at 2601248 with start_time 0,
fifo_time 2601301
[ 2901.254162] Queue f36a2700 added at 2601254 with start_time 0,
fifo_time 2601301
[ 2901.266267] Queue f36a2700 added at 2601266 with start_time 0,
fifo_time 2601301
[ 2901.274044] Queue f36a2700 added at 2601274 with start_time 0,
fifo_time 2601301
[ 2901.276767] Queue f36a2700 added at 2601276 with start_time 0,
fifo_time 2601301
[ 2901.287135] Queue f36a2700 added at 2601287 with start_time 0,
fifo_time 2601301
[ 2901.294752] Queue f36a2700 added at 2601294 with start_time 0,
fifo_time 2601301
[ 2901.296890] Queue f36a2700 added at 2601296 with start_time 0,
fifo_time 2601301
[ 2901.309032] Queue f36a2700 added at 2601309 with start_time 0,
fifo_time 2601301
[ 2901.418604] Queue f36a2694 added at 2601418 with start_time
2601407, fifo_time 2601532
[ 2901.429552] Queue f36a2dc0 added at 2601429 with start_time 0,
fifo_time 2601529
[ 2901.442382] Queue f36a2dc0 added at 2601442 with start_time 0,
fifo_time 2601529
[ 2901.451290] Queue f36a2dc0 added at 2601451 with start_time 0,
fifo_time 2601529
[ 2901.457910] Queue f36a2dc0 added at 2601457 with start_time 0,
fifo_time 2601529
[ 2901.470146] Queue f36a2dc0 added at 2601470 with start_time 0,
fifo_time 2601529
[ 2901.476499] Queue f36a2dc0 added at 2601476 with start_time 0,
fifo_time 2601529
[ 2901.484636] Queue f36a2dc0 added at 2601484 with start_time 0,
fifo_time 2601529
[ 2901.493999] Queue f36a2dc0 added at 2601493 with start_time 0,
fifo_time 2601529
[ 2901.501657] Queue f36a2dc0 added at 2601501 with start_time 0,
fifo_time 2601529
[ 2901.505033] Queue f36a2dc0 added at 2601504 with start_time 0,
fifo_time 2601529
[ 2901.511003] Queue f36a2dc0 added at 2601510 with start_time 0,
fifo_time 2601529
[ 2901.516789] Queue f36a2dc0 added at 2601516 with start_time 0,
fifo_time 2601529
[ 2901.526158] Queue f36a2dc0 added at 2601526 with start_time 0,
fifo_time 2601529
[ 2901.536981] Queue f36a2dc0 added at 2601536 with start_time 0,
fifo_time 2601529
[ 2901.551037] Queue f36a2700 added at 2601551 with start_time 0,
fifo_time 2601650
[ 2901.562150] Queue f36a2700 added at 2601562 with start_time 0,
fifo_time 2601650
[ 2901.567243] Queue f36a2700 added at 2601567 with start_time 0,
fifo_time 2601650
[ 2901.574150] Queue f36a2700 added at 2601574 with start_time 0,
fifo_time 2601650
[ 2901.578523] Queue f36a2700 added at 2601578 with start_time 0,
fifo_time 2601650
[ 2901.588526] Queue f36a2700 added at 2601588 with start_time 0,
fifo_time 2601650
[ 2901.615982] Queue f36a2694 added at 2601615 with start_time 1,
fifo_time 2601698
[ 2901.701074] Queue f36a2694 added at 2601701 with start_time
2601690, fifo_time 2601815
[ 2901.710993] Queue f36a2700 added at 2601710 with start_time 0,
fifo_time 2601810
[ 2901.720751] Queue f36a2700 added at 2601720 with start_time 0,
fifo_time 2601810
[ 2901.728237] Queue f36a2700 added at 2601728 with start_time 0,
fifo_time 2601810
[ 2901.739622] Queue f36a2700 added at 2601739 with start_time 0,
fifo_time 2601810
[ 2901.747369] Queue f36a2700 added at 2601747 with start_time 0,
fifo_time 2601810
[ 2901.756372] Queue f36a2700 added at 2601756 with start_time 0,
fifo_time 2601810
[ 2901.767507] Queue f36a2700 added at 2601767 with start_time 0,
fifo_time 2601810
[ 2901.773621] Queue f36a2700 added at 2601773 with start_time 0,
fifo_time 2601810
[ 2901.784752] Queue f36a2700 added at 2601784 with start_time 0,
fifo_time 2601810
[ 2901.791117] Queue f36a2700 added at 2601791 with start_time 0,
fifo_time 2601810
[ 2901.800506] Queue f36a2700 added at 2601800 with start_time 0,
fifo_time 2601810
[ 2901.806108] Queue f36a2700 added at 2601806 with start_time 0,
fifo_time 2601810
[ 2901.816634] Queue f36a2700 added at 2601816 with start_time 0,
fifo_time 2601810
[ 2901.830011] Queue f36a2dc0 added at 2601829 with start_time 0,
fifo_time 2601929
[ 2901.841172] Queue f36a2dc0 added at 2601841 with start_time 0,
fifo_time 2601929
[ 2901.849320] Queue f36a2dc0 added at 2601849 with start_time 0,
fifo_time 2601929
[ 2901.859641] Queue f36a2dc0 added at 2601859 with start_time 0,
fifo_time 2601929
[ 2901.868768] Queue f36a2dc0 added at 2601868 with start_time 0,
fifo_time 2601929
[ 2901.880052] Queue f36a2dc0 added at 2601880 with start_time 0,
fifo_time 2601929
[ 2901.885278] Queue f36a2dc0 added at 2601885 with start_time 0,
fifo_time 2601929
[ 2901.893273] Queue f36a2dc0 added at 2601893 with start_time 0,
fifo_time 2601929
[ 2901.900390] Queue f36a2dc0 added at 2601900 with start_time 0,
fifo_time 2601929
[ 2901.910893] Queue f36a2dc0 added at 2601910 with start_time 0,
fifo_time 2601929
[ 2901.917888] Queue f36a2dc0 added at 2601917 with start_time 0,
fifo_time 2601929
[ 2901.926031] Queue f36a2dc0 added at 2601926 with start_time 0,
fifo_time 2601929
[ 2901.932151] Queue f36a2dc0 added at 2601932 with start_time 0,
fifo_time 2601929
[ 2901.998417] Queue f36a2694 added at 2601998 with start_time 1,
fifo_time 2602045
[ 2902.047930] Queue f36a2694 added at 2602047 with start_time
2602037, fifo_time 2602162
[ 2902.056985] Queue f36a2700 added at 2602056 with start_time 0, fifo_time 0
[ 2902.148427] Queue f36a2694 added at 2602148 with start_time 1,
fifo_time 2602157
[ 2902.157051] Queue f36a2694 added at 2602157 with start_time
2602148, fifo_time 2602273
[ 2902.172470] Queue f36a2dc0 added at 2602172 with start_time 0,
fifo_time 2602272
[ 2902.182978] Queue f36a2dc0 added at 2602182 with start_time 0,
fifo_time 2602272
[ 2902.197989] Queue f36a2dc0 added at 2602197 with start_time 0,
fifo_time 2602272
[ 2902.208464] Queue f36a2dc0 added at 2602208 with start_time 0,
fifo_time 2602272
[ 2902.219344] Queue f36a2dc0 added at 2602219 with start_time 0,
fifo_time 2602272
[ 2902.225239] Queue f36a2dc0 added at 2602225 with start_time 0,
fifo_time 2602272
[ 2902.232345] Queue f36a2dc0 added at 2602232 with start_time 0,
fifo_time 2602272
[ 2902.238079] Queue f36a2dc0 added at 2602238 with start_time 0,
fifo_time 2602272
[ 2902.245393] Queue f36a2dc0 added at 2602245 with start_time 0,
fifo_time 2602272
[ 2902.251997] Queue f36a2dc0 added at 2602251 with start_time 0,
fifo_time 2602272
[ 2902.259211] Queue f36a2dc0 added at 2602259 with start_time 0,
fifo_time 2602272
[ 2902.271594] Queue f36a2dc0 added at 2602271 with start_time 0,
fifo_time 2602272
[ 2902.278868] Queue f36a2dc0 added at 2602278 with start_time 0,
fifo_time 2602272
[ 2902.293854] Queue f36a2700 added at 2602293 with start_time 0,
fifo_time 2602393
[ 2902.300962] Queue f36a2700 added at 2602300 with start_time 0,
fifo_time 2602393
[ 2902.305826] Queue f36a2700 added at 2602305 with start_time 0,
fifo_time 2602393
[ 2902.310847] Queue f36a2700 added at 2602310 with start_time 0,
fifo_time 2602393
[ 2902.317337] Queue f36a2700 added at 2602317 with start_time 0,
fifo_time 2602393
[ 2902.325590] Queue f36a2700 added at 2602325 with start_time 0,
fifo_time 2602393
[ 2902.335340] Queue f36a2700 added at 2602335 with start_time 0,
fifo_time 2602393
[ 2902.347267] Queue f36a2700 added at 2602347 with start_time 0,
fifo_time 2602393
[ 2902.356614] Queue f36a2700 added at 2602356 with start_time 0,
fifo_time 2602393
[ 2902.362082] Queue f36a2700 added at 2602362 with start_time 0,
fifo_time 2602393
[ 2902.375340] Queue f36a2700 added at 2602375 with start_time 0,
fifo_time 2602393
[ 2902.391207] Queue f36a2700 added at 2602391 with start_time 0,
fifo_time 2602393
[ 2902.399966] Queue f36a2700 added at 2602399 with start_time 0,
fifo_time 2602393
[ 2902.515413] Queue f36a2694 added at 2602515 with start_time
2602504, fifo_time 2602629
[ 2902.531346] Queue f36a2dc0 added at 2602531 with start_time 0,
fifo_time 2602631
[ 2902.536692] Queue f36a2dc0 added at 2602536 with start_time 0,
fifo_time 2602631
[ 2902.540470] Queue f36a2dc0 added at 2602540 with start_time 0,
fifo_time 2602631
[ 2902.546630] Queue f36a2dc0 added at 2602546 with start_time 0,
fifo_time 2602631
[ 2902.551987] Queue f36a2dc0 added at 2602551 with start_time 0,
fifo_time 2602631
[ 2902.558467] Queue f36a2dc0 added at 2602558 with start_time 0,
fifo_time 2602631
[ 2902.566719] Queue f36a2dc0 added at 2602566 with start_time 0,
fifo_time 2602631
[ 2902.576452] Queue f36a2dc0 added at 2602576 with start_time 0,
fifo_time 2602631
[ 2902.585818] Queue f36a2dc0 added at 2602585 with start_time 0,
fifo_time 2602631
[ 2902.591323] Queue f36a2dc0 added at 2602591 with start_time 0,
fifo_time 2602631
[ 2902.596935] Queue f36a2dc0 added at 2602596 with start_time 0,
fifo_time 2602631
[ 2902.604066] Queue f36a2dc0 added at 2602604 with start_time 0,
fifo_time 2602631
[ 2902.612820] Queue f36a2dc0 added at 2602612 with start_time 0,
fifo_time 2602631
[ 2902.619764] Queue f36a2dc0 added at 2602619 with start_time 0,
fifo_time 2602631
[ 2902.623096] Queue f36a2dc0 added at 2602623 with start_time 0,
fifo_time 2602631
[ 2902.634605] Queue f36a2dc0 added at 2602634 with start_time 0,
fifo_time 2602631
[ 2902.646341] Queue f36a2700 added at 2602646 with start_time 0,
fifo_time 2602746
[ 2902.654590] Queue f36a2700 added at 2602654 with start_time 0,
fifo_time 2602746
[ 2902.661063] Queue f36a2700 added at 2602661 with start_time 0,
fifo_time 2602746
[ 2902.668204] Queue f36a2700 added at 2602668 with start_time 0,
fifo_time 2602746
[ 2902.686868] Queue f36a2694 added at 2602686 with start_time 1,
fifo_time 2602777
[ 2902.777273] Queue f36a2694 added at 2602777 with start_time
2602766, fifo_time 2602891
[ 2902.791832] Queue f36a2700 added at 2602791 with start_time 0,
fifo_time 2602891
[ 2902.804069] Queue f36a2700 added at 2602804 with start_time 0,
fifo_time 2602891
[ 2902.816080] Queue f36a2700 added at 2602816 with start_time 0,
fifo_time 2602891
[ 2902.822437] Queue f36a2700 added at 2602822 with start_time 0,
fifo_time 2602891
[ 2902.827809] Queue f36a2700 added at 2602827 with start_time 0,
fifo_time 2602891
[ 2902.835191] Queue f36a2700 added at 2602835 with start_time 0,
fifo_time 2602891
[ 2902.845092] Queue f36a2700 added at 2602845 with start_time 0,
fifo_time 2602891
[ 2902.853156] Queue f36a2700 added at 2602852 with start_time 0,
fifo_time 2602891
[ 2902.860446] Queue f36a2700 added at 2602860 with start_time 0,
fifo_time 2602891
[ 2902.869308] Queue f36a2700 added at 2602869 with start_time 0,
fifo_time 2602891
[ 2902.877688] Queue f36a2700 added at 2602877 with start_time 0,
fifo_time 2602891
[ 2902.890431] Queue f36a2700 added at 2602890 with start_time 0,
fifo_time 2602891
[ 2902.896071] Queue f36a2700 added at 2602896 with start_time 0,
fifo_time 2602891
[ 2902.907181] Queue f36a2dc0 added at 2602907 with start_time 0,
fifo_time 2603007
[ 2902.917954] Queue f36a2dc0 added at 2602917 with start_time 0,
fifo_time 2603007
[ 2902.923808] Queue f36a2dc0 added at 2602923 with start_time 0,
fifo_time 2603007
[ 2902.932822] Queue f36a2dc0 added at 2602932 with start_time 0,
fifo_time 2603007
[ 2902.937797] Queue f36a2dc0 added at 2602937 with start_time 0,
fifo_time 2603007
[ 2902.946325] Queue f36a2dc0 added at 2602946 with start_time 0,
fifo_time 2603007
[ 2902.958563] Queue f36a2dc0 added at 2602958 with start_time 0,
fifo_time 2603007
[ 2902.968192] Queue f36a2dc0 added at 2602968 with start_time 0,
fifo_time 2603007
[ 2902.973697] Queue f36a2dc0 added at 2602973 with start_time 0,
fifo_time 2603007
[ 2902.980952] Queue f36a2dc0 added at 2602980 with start_time 0,
fifo_time 2603007
[ 2902.990088] Queue f36a2dc0 added at 2602990 with start_time 0,
fifo_time 2603007
[ 2903.000123] Queue f36a2dc0 added at 2603000 with start_time 0,
fifo_time 2603007
[ 2903.009221] Queue f36a2dc0 added at 2603009 with start_time 0,
fifo_time 2603007
[ 2903.063339] Queue f36a2694 added at 2603063 with start_time 1,
fifo_time 2603119
[ 2903.121501] Queue f36a2694 added at 2603121 with start_time
2603110, fifo_time 2603235
[ 2903.135307] Queue f36a2700 added at 2603135 with start_time 0,
fifo_time 2603235
[ 2903.143354] Queue f36a2700 added at 2603143 with start_time 0,
fifo_time 2603235
[ 2903.153077] Queue f36a2700 added at 2603153 with start_time 0,
fifo_time 2603235
[ 2903.162585] Queue f36a2700 added at 2603162 with start_time 0,
fifo_time 2603235
[ 2903.226085] Queue f36a2694 added at 2603226 with start_time 1,
fifo_time 2603263
[ 2903.264869] Queue f36a2694 added at 2603264 with start_time
2603254, fifo_time 2603379
[ 2903.279694] Queue f36a2dc0 added at 2603279 with start_time 0,
fifo_time 2603379
[ 2903.285062] Queue f36a2dc0 added at 2603285 with start_time 0,
fifo_time 2603379
[ 2903.296662] Queue f36a2dc0 added at 2603296 with start_time 0,
fifo_time 2603379
[ 2903.303988] Queue f36a2dc0 added at 2603303 with start_time 0,
fifo_time 2603379
[ 2903.316188] Queue f36a2dc0 added at 2603316 with start_time 0,
fifo_time 2603379
[ 2903.323045] Queue f36a2dc0 added at 2603322 with start_time 0,
fifo_time 2603379
[ 2903.328795] Queue f36a2dc0 added at 2603328 with start_time 0,
fifo_time 2603379
[ 2903.334688] Queue f36a2dc0 added at 2603334 with start_time 0,
fifo_time 2603379
[ 2903.346453] Queue f36a2dc0 added at 2603346 with start_time 0,
fifo_time 2603379
[ 2903.358062] Queue f36a2dc0 added at 2603358 with start_time 0,
fifo_time 2603379
[ 2903.363410] Queue f36a2dc0 added at 2603363 with start_time 0,
fifo_time 2603379
[ 2903.369163] Queue f36a2dc0 added at 2603369 with start_time 0,
fifo_time 2603379
[ 2903.375191] Queue f36a2dc0 added at 2603375 with start_time 0,
fifo_time 2603379
[ 2903.389201] Queue f36a2dc0 added at 2603389 with start_time 0,
fifo_time 2603379
[ 2903.398676] Queue f36a2700 added at 2603398 with start_time 0,
fifo_time 2603498
[ 2903.404920] Queue f36a2700 added at 2603404 with start_time 0,
fifo_time 2603498
[ 2903.412293] Queue f36a2700 added at 2603412 with start_time 0,
fifo_time 2603498
[ 2903.421186] Queue f36a2700 added at 2603421 with start_time 0,
fifo_time 2603498
[ 2903.426661] Queue f36a2700 added at 2603426 with start_time 0,
fifo_time 2603498
[ 2903.439177] Queue f36a2700 added at 2603438 with start_time 0,
fifo_time 2603498
[ 2903.446128] Queue f36a2700 added at 2603445 with start_time 0,
fifo_time 2603498
[ 2903.453804] Queue f36a2700 added at 2603453 with start_time 0,
fifo_time 2603498

i.e. start_time is almost always small or 0. fifo_time is usually
correct, but may be 0 as well.
unfortunately, this time I have no clue on the possible cause.

Corrado

>
> --
> Jens Axboe
>
>



-- 
__________________________________________________________________________

dott. Corrado Zoccolo                          mailto:czoccolo@gmail.com
PhD - Department of Computer Science - University of Pisa, Italy
--------------------------------------------------------------------------

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: bug in elevator/cfq regarding start_time?
  2009-10-05 15:08   ` Corrado Zoccolo
@ 2009-10-05 20:26     ` Corrado Zoccolo
  2009-10-06  7:12       ` Jens Axboe
  0 siblings, 1 reply; 7+ messages in thread
From: Corrado Zoccolo @ 2009-10-05 20:26 UTC (permalink / raw)
  To: Jens Axboe; +Cc: Linux-Kernel

On Mon, Oct 5, 2009 at 5:08 PM, Corrado Zoccolo <czoccolo@gmail.com> wrote:
> On Sun, Oct 4, 2009 at 10:59 PM, Jens Axboe <jens.axboe@oracle.com> wrote:
>> Good spotting! So we can either add the same copy in cfq, or we can just
>> move the ->start_time check and assignment in attempt_merge() to post
>> the elv_merge_requests() call. I think the latter would work fine, but
>> I'll check and fix tomorrow.
>
> I think there is still something buggy regarding those timestamps.
False alarm. I just found that the list was not yet filled at that
place in the code.

Corrado

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: bug in elevator/cfq regarding start_time?
  2009-10-05 20:26     ` Corrado Zoccolo
@ 2009-10-06  7:12       ` Jens Axboe
  2009-10-06  8:43         ` Corrado Zoccolo
  0 siblings, 1 reply; 7+ messages in thread
From: Jens Axboe @ 2009-10-06  7:12 UTC (permalink / raw)
  To: Corrado Zoccolo; +Cc: Linux-Kernel

On Mon, Oct 05 2009, Corrado Zoccolo wrote:
> On Mon, Oct 5, 2009 at 5:08 PM, Corrado Zoccolo <czoccolo@gmail.com> wrote:
> > On Sun, Oct 4, 2009 at 10:59 PM, Jens Axboe <jens.axboe@oracle.com> wrote:
> >> Good spotting! So we can either add the same copy in cfq, or we can just
> >> move the ->start_time check and assignment in attempt_merge() to post
> >> the elv_merge_requests() call. I think the latter would work fine, but
> >> I'll check and fix tomorrow.
> >
> > I think there is still something buggy regarding those timestamps.
> False alarm. I just found that the list was not yet filled at that
> place in the code.

OK, it did look a bit puzzling. FWIW, this is what I committed
yesterday:

http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=30996f40bffe73f05abb92a4cec254befa8cecf7

-- 
Jens Axboe


^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: bug in elevator/cfq regarding start_time?
  2009-10-06  7:12       ` Jens Axboe
@ 2009-10-06  8:43         ` Corrado Zoccolo
  2009-10-06  8:54           ` Jens Axboe
  0 siblings, 1 reply; 7+ messages in thread
From: Corrado Zoccolo @ 2009-10-06  8:43 UTC (permalink / raw)
  To: Jens Axboe; +Cc: Linux-Kernel

On Tue, Oct 6, 2009 at 9:12 AM, Jens Axboe <jens.axboe@oracle.com> wrote:
> On Mon, Oct 05 2009, Corrado Zoccolo wrote:
>> On Mon, Oct 5, 2009 at 5:08 PM, Corrado Zoccolo <czoccolo@gmail.com> wrote:
>> False alarm. I just found that the list was not yet filled at that
>> place in the code.
>
> OK, it did look a bit puzzling. FWIW, this is what I committed
> yesterday:
>
> http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=30996f40bffe73f05abb92a4cec254befa8cecf7
Yes, I was testing this one, but put the testing code in the wrong place.
After fixing the testing code, I verified it is working correctly.
Now, both the start time and fifo_time are monotonic.

Thanks,
Corrado
>
> --
> Jens Axboe
>
>

^ permalink raw reply	[flat|nested] 7+ messages in thread

* Re: bug in elevator/cfq regarding start_time?
  2009-10-06  8:43         ` Corrado Zoccolo
@ 2009-10-06  8:54           ` Jens Axboe
  0 siblings, 0 replies; 7+ messages in thread
From: Jens Axboe @ 2009-10-06  8:54 UTC (permalink / raw)
  To: Corrado Zoccolo; +Cc: Linux-Kernel

On Tue, Oct 06 2009, Corrado Zoccolo wrote:
> On Tue, Oct 6, 2009 at 9:12 AM, Jens Axboe <jens.axboe@oracle.com> wrote:
> > On Mon, Oct 05 2009, Corrado Zoccolo wrote:
> >> On Mon, Oct 5, 2009 at 5:08 PM, Corrado Zoccolo <czoccolo@gmail.com> wrote:
> >> False alarm. I just found that the list was not yet filled at that
> >> place in the code.
> >
> > OK, it did look a bit puzzling. FWIW, this is what I committed
> > yesterday:
> >
> > http://git.kernel.dk/?p=linux-2.6-block.git;a=commit;h=30996f40bffe73f05abb92a4cec254befa8cecf7
> Yes, I was testing this one, but put the testing code in the wrong place.
> After fixing the testing code, I verified it is working correctly.
> Now, both the start time and fifo_time are monotonic.

OK good, thanks for confirming! I'll push it for 2.6.32. And thanks for
spotting this in the first place, the fixing part was the easy bit.

-- 
Jens Axboe


^ permalink raw reply	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2009-10-06  8:54 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2009-10-04 20:54 bug in elevator/cfq regarding start_time? Corrado Zoccolo
2009-10-04 20:59 ` Jens Axboe
2009-10-05 15:08   ` Corrado Zoccolo
2009-10-05 20:26     ` Corrado Zoccolo
2009-10-06  7:12       ` Jens Axboe
2009-10-06  8:43         ` Corrado Zoccolo
2009-10-06  8:54           ` Jens Axboe

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