From mboxrd@z Thu Jan  1 00:00:00 1970
From: axboe@kernel.dk (Jens Axboe)
Date: Fri, 14 Dec 2018 11:50:25 -0700
Subject: [PATCH] nvme-pci: only set nr_maps to 2 if poll queues are
 supported
In-Reply-To: <9d2fa9e4-927e-655b-5db3-32d8f0a17db7@grimberg.me>
References: <20181214162019.14847-1-hch@lst.de>
 <9d2fa9e4-927e-655b-5db3-32d8f0a17db7@grimberg.me>
Message-ID: <e6ff4bc1-2fbe-9aef-a384-ee19b4788460@kernel.dk>

On 12/14/18 11:43 AM, Sagi Grimberg wrote:
> 
>> The block layer now enables polling support on a queue if nr_maps
>> includes the poll map, so we should only set that if we actually
>> support poll queues.
>>
>> Fixes:  6544d229bf ("block: enable polling by default if a poll map is initalized")
> 
> What does it fix? is there a bug when setting 3 queue maps?

After the recent changes, blk_mq_init_allocated_queue() does this:

if (set->nr_maps > HCTX_TYPE_POLL)
	blk_queue_flag_set(QUEUE_FLAG_POLL, q);

since the core doesn't have any notion of how many queues are used for
what. We only support polling if you have explicit poll queues now,
hence the above is wrong if nvme says nr_maps is 3 and it doesn't have
any poll queues.

-- 
Jens Axboe