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Subject: Re: [PATCH] block/bfq: fix ifdef for CONFIG_BFQ_GROUP_IOSCHED=y
To:     Jens Axboe <axboe@kernel.dk>,
        Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
        linux-block@vger.kernel.org,
        Paolo Valente <paolo.valente@linaro.org>,
        linux-kernel@vger.kernel.org
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 <5234a971-2b6a-47b1-0071-8f3bd07d9fc3@kernel.dk>
From:   =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= <holger@applied-asynchrony.com>
Organization: Applied Asynchrony, Inc.
Message-ID: <cf0dc6b2-6ecf-c895-6c21-8746700bdae4@applied-asynchrony.com>
Date:   Fri, 29 Mar 2019 17:12:43 +0100
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On 3/29/19 4:58 PM, Jens Axboe wrote:
> On 3/29/19 9:56 AM, Holger Hoffstätte wrote:
>> On 3/29/19 3:01 PM, Konstantin Khlebnikov wrote:
>>> Replace BFQ_GROUP_IOSCHED_ENABLED with CONFIG_BFQ_GROUP_IOSCHED.
>>> Code under these ifdefs never worked, something might be broken.
>>>
>>> Fixes: 0471559c2fbd ("block, bfq: add/remove entity weights correctly")
>>> Fixes: 73d58118498b ("block, bfq: consider also ioprio classes in symmetry detection")
>>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
>>> ---
>>>    block/bfq-iosched.c |    2 +-
>>>    block/bfq-wf2q.c    |    2 +-
>>>    2 files changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
>>> index 4c592496a16a..fac188dd78fa 100644
>>> --- a/block/bfq-iosched.c
>>> +++ b/block/bfq-iosched.c
>>> @@ -674,7 +674,7 @@ static bool bfq_symmetric_scenario(struct bfq_data *bfqd)
>>>    	 * at least two nodes.
>>>    	 */
>>>    	return !(varied_queue_weights || multiple_classes_busy
>>> -#ifdef BFQ_GROUP_IOSCHED_ENABLED
>>> +#ifdef CONFIG_BFQ_GROUP_IOSCHED
>>>    	       || bfqd->num_groups_with_pending_reqs > 0
>>>    #endif
>>>    		);
>>> diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c
>>> index 63311d1ff1ed..a11bef75483d 100644
>>> --- a/block/bfq-wf2q.c
>>> +++ b/block/bfq-wf2q.c
>>> @@ -1012,7 +1012,7 @@ static void __bfq_activate_entity(struct bfq_entity *entity,
>>>    		entity->on_st = true;
>>>    	}
>>>    
>>> -#ifdef BFQ_GROUP_IOSCHED_ENABLED
>>> +#ifdef CONFIG_BFQ_GROUP_IOSCHED
>>>    	if (!bfq_entity_to_bfqq(entity)) { /* bfq_group */
>>>    		struct bfq_group *bfqg =
>>>    			container_of(entity, struct bfq_group, entity);
>>>
>>>
>>
>> Good catch! I run without group scheduling and therefore didn't notice these
>> stray defines earlier. For 5.1 it should merge cleanly; adding this on top of
>> the pending 5.2 BFQ patches required a small context fixup in hunk #1 due to
>> "block, bfq: do not idle for lowest-weight queues".
> 
> I'm hesitant to apply this, since the group scheduling stuff has obviously never
> been tested.

This is simply a regression in 5.1 caused by 73d58118498b - nothing else,
and as such this fix needs to go into 5.1 as well. I'm sure Paolo will agree.
What you so ominously  call "the group scheduling stuff" has been there and
shipping in mainline since day 1 of the BFQ merge, and it works fine in 5.0.

cheers
Holger