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Subject: Re: [REGRESSION] bfq probe failed on 4.19-rc3
To:     Takashi Iwai <tiwai@suse.de>
Cc:     Jeff Moyer <jmoyer@redhat.com>,
        Paolo Valente <paolo.valente@linaro.org>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
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 <8d5f3ab2-50e8-226c-8ccb-c722872910db@kernel.dk>
 <s5hbm936qii.wl-tiwai@suse.de>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <6e932598-3e24-3918-a600-eb162a475ea3@kernel.dk>
Date:   Wed, 12 Sep 2018 08:31:18 -0600
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On 9/12/18 2:58 AM, Takashi Iwai wrote:
> On Tue, 11 Sep 2018 18:54:19 +0200,
> Jens Axboe wrote:
>>
>> On 9/11/18 10:51 AM, Jeff Moyer wrote:
>>> Jens Axboe <axboe@kernel.dk> writes:
>>>
>>>> On 9/11/18 10:48 AM, Jeff Moyer wrote:
>>>>> Jens Axboe <axboe@kernel.dk> writes:
>>>>>
>>>>>> On 9/11/18 10:03 AM, Takashi Iwai wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> I noticed that bfq doesn't appear in the I/O scheduler list on
>>>>>>> 4.19-rc3.  It seems that blkcg_policy_register() at the beginning of
>>>>>>> bfq_init() returns -ENOSPC, hence the probe aborts silently.
>>>>>>>
>>>>>>> Is this already addressed?
>>>>>>
>>>>>> Haven't heard about this one before. What kernel did you last use that
>>>>>> worked?
>>>>>
>>>>> I'm guessing you just need to update the maximum number of policies:
>>>>>
>>>>> /*
>>>>>  * Maximum number of blkcg policies allowed to be registered concurrently.
>>>>>  * Defined here to simplify include dependency.
>>>>>  */
>>>>> #define BLKCG_MAX_POLS          3
>>>>
>>>> That is my guess too, hence the suggestion to try and disable the
>>>> iolatency policy. Just tried here without, and it works, rebooting
>>>> with to verify that we're running out of policy slots.
>>>
>>> Functions calling this function: blkcg_policy_register
>>>
>>>   File                      Function       Line
>>> 0 block/bfq-iosched.c       bfq_init       5675 ret =
>>>                                                 blkcg_policy_register(&blkcg_pol
>>>                                                 icy_bfq);
>>> 1 block/blk-iolatency.c     iolatency_init  946 return
>>>                                                 blkcg_policy_register(&blkcg_pol
>>>                                                 icy_iolatency);
>>> 2 block/blk-throttle.c      throtl_init    2511 return
>>>                                                 blkcg_policy_register(&blkcg_pol
>>>                                                 icy_throtl);
>>> 3 block/cfq-iosched.c       cfq_init       4869 ret =
>>>                                                 blkcg_policy_register(&blkcg_pol
>>>                                                 icy_cfq);
>>>
>>> And then there were 4...
>>
>> Exactly. I'd bump it to 5 to leave room for one more, if we have to grow it
>> again, probably worth it to make it dynamic. So for, not really needed. Takashi,
>> can verify that the below fixes it up for you?
> 
> Yes, it works.
> 
> Tested-by: Takashi Iwai <tiwai@suse.de>

Thanks for verifying (and reporting), I'll get this in for 4.19-rc4.

-- 
Jens Axboe