Re: blk-mq request allocation stalls [was: Re: [PATCH v3 0/8] dm: add request-based blk-mq support]

[Mike Snitzer <snitzer@redhat.com>]

On Fri, Jan 09 2015 at  4:56pm -0500,
Jens Axboe <axboe@kernel.dk> wrote:

> On 01/09/2015 02:40 PM, Mike Snitzer wrote:
> >On Fri, Jan 09 2015 at  4:11pm -0500,
> >Jens Axboe <axboe@kernel.dk> wrote:
> >
> >>
> >>Actually, try this one instead, it should be a bit more precise than
> >>the first.
> >>
> >
> >Thanks for the test patch.
> >
> >I'm still seeing failures that look wrong (last_tag=127 could be edge
> >condition not handled properly?):
> >
> >[   14.254632] __bt_get: values before for loop: last_tag=127, index=3
> >[   14.255841] __bt_get: values after  for loop: last_tag=64, index=2
> >[   14.257036]
> >[   14.257036] bt_get: __bt_get() returned -1
> >[   14.258051] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> >[   14.259246] nr_free=128, nr_reserved=0
> >[   14.259963] active_queues=0
> >
> >[  213.115997] __bt_get: values before for loop: last_tag=127, index=3
> >[  213.117115] __bt_get: values after  for loop: last_tag=96, index=3
> >[  213.118200]
> >[  213.118200] bt_get: __bt_get() returned -1
> >[  213.121593] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> >[  213.123960] nr_free=128, nr_reserved=0
> >[  213.125880] active_queues=0
> >
> >[  239.158079] __bt_get: values before for loop: last_tag=8, index=0
> >[  239.160363] __bt_get: values after  for loop: last_tag=0, index=0
> >[  239.162896]
> >[  239.162896] bt_get: __bt_get() returned -1
> >[  239.166284] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> >[  239.168623] nr_free=127, nr_reserved=0
> >[  239.170508] active_queues=0
> 
> Thanks for testing, can you try this one?

Huh, at least now we're now seeing some nr_free=0... but the last 3
failures below look unnecessary still.  E.g. the last_tag=127 case

[   13.895265] __bt_get: values before for loop: last_tag=59, index=1
[   13.895265] __bt_get: values after  for loop: last_tag=32, index=1
[   13.895266] 
[   13.895266] bt_get: __bt_get() returned -1
[   13.895267] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
[   13.895267] nr_free=0, nr_reserved=0
[   13.895268] active_queues=0

[   13.895269] __bt_get: values before for loop: last_tag=0, index=0
[   13.895270] __bt_get: values after  for loop: last_tag=0, index=0
[   13.895270] 
[   13.895270] bt_get: __bt_get() returned -1
[   13.895271] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
[   13.895272] nr_free=0, nr_reserved=0
[   13.895272] active_queues=0
[   13.895324] __bt_get: values before for loop: last_tag=0, index=0
[   13.895324] __bt_get: values after  for loop: last_tag=0, index=0
[   13.895325] bt_get: __bt_get() _still_ returned -1
[   13.895325] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
[   13.895326] nr_free=0, nr_reserved=0
[   13.895326] active_queues=0

[   18.931425] __bt_get: values before for loop: last_tag=127, index=3
[   18.933317] __bt_get: values after  for loop: last_tag=0, index=0
[   18.935140] 
[   18.935140] bt_get: __bt_get() returned -1
[   18.936807] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
[   18.938772] nr_free=128, nr_reserved=0
[   18.939927] active_queues=0

[  489.119597] __bt_get: values before for loop: last_tag=95, index=2
[  489.120621] __bt_get: values after  for loop: last_tag=96, index=3
[  489.121624]
[  489.121624] bt_get: __bt_get() returned -1
[  489.122532] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
[  489.123581] nr_free=128, nr_reserved=0
[  489.124206] active_queues=0

[  494.705758] __bt_get: values before for loop: last_tag=127, index=3
[  494.707797] __bt_get: values after  for loop: last_tag=0, index=0
[  494.709696] 
[  494.709696] bt_get: __bt_get() returned -1
[  494.712459] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
[  494.714403] nr_free=128, nr_reserved=0
[  494.715955] active_queues=0