From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jens Axboe <axboe@kernel.dk>
Subject: Re: blk-mq request allocation stalls
Date: Mon, 12 Jan 2015 09:34:21 -0700
Message-ID: <54B3F78D.2020704@kernel.dk>
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To: Bart Van Assche <bart.vanassche@sandisk.com>, Mike Snitzer <snitzer@redhat.com>
Cc: Keith Busch <keith.busch@intel.com>, Christoph Hellwig <hch@infradead.org>, device-mapper development <dm-devel@redhat.com>, Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
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On 01/12/2015 09:12 AM, Bart Van Assche wrote:
> On 01/12/15 16:42, Jens Axboe wrote:
>> On 01/12/2015 07:46 AM, Bart Van Assche wrote:
>>> bt_get: __bt_get() returned -1
>>> queue_num=2, nr_tags=62, reserved_tags=0, bits_per_word=3
>>> nr_free=62, nr_reserved=0, may_queue=0
>>> active_queues=8
>>
>> Can you add dumping of hctx->nr_active when this fails? You case is that
>> the may_queue logic says no-can-do, so it smells like the nr_active
>> accounting is wonky since you have supposedly no allocated tags, yet it
>> clearly thinks that you do.
>
> Hello Jens,
>
> The requested output is as follows:
>
> bt_get: __bt_get() returned -1
> queue_num=0, nr_tags=62, reserved_tags=0, bits_per_word=3
> nr_free=62, nr_reserved=0, hctx->tags->active_queues=7,
> hctx->nr_active=9, hctx_may_queue()=0
> active_queues=7

So that does look a bit off, we have (supposedly) 9 active requests, but 
nothing allocated. When the mkfs is done and things are idle, can you 
try and cat the 'active' file in the mq directory? I want to see if it 
drops to zero or stays elevated.

-- 
Jens Axboe