From: Logan Gunthorpe <logang@deltatee.com>
To: Sagi Grimberg <sagi@grimberg.me>,
Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>,
linux-nvme@lists.infradead.org
Cc: hch@lst.de
Subject: Re: [PATCH 0/1] nvmet: allow user to set req alloc flag
Date: Tue, 20 Oct 2020 09:39:28 -0600 [thread overview]
Message-ID: <a37ee655-c215-2354-4d55-267b11d92ae0@deltatee.com> (raw)
In-Reply-To: <74e2bc85-3752-08fe-4f2c-07130ab4411d@grimberg.me>
On 2020-10-20 2:22 a.m., Sagi Grimberg wrote:
>
>> Hi,
>>
>> When using NVMeOF target in the passthru mode we allocate the request
>> with BLK_MQ_REQ_NOWAIT flag. This allocates the request in the following
>> manner :-
>>
>> nvme_alloc_request()
>> blk_mq_alloc_rquest()
>> blk_mq_queue_enter()
>> if (flag & BLK_MQ_REQ_NOWAIT)
>> return -EBUSY; <-- return if busy.
>>
>> On the NVMe controller which I've the fio random write workload running
>> parallel on 32 namespaces with higher queue depth results in I/O error,
>> where blk_mq_queue_enter() returning -EBUSY as shown above. This problem
>> is not easy to reproduce but occurs once in a while with following error
>> (See 1 for detailed log) :-
>>
>> test1: (groupid=0, jobs=32): err= 5
>> (file:io_u.c:1744, func=io_u error, error=Input/output error):
>>
>> When the flag BLK_MQ_REQ_NOWAIT is removed from the allocation the
>> workload doen't result in the error.
>>
>> This patch fixes the problem with the request allocation by adding
>> a new configfs attribute so that user can optionally decide whether
>> to use BLK_MQ_REQ_NOWAIT or not. We retain the default behavior by
>> using BLK_MQ_REQ_NOWAIT when creating the nvmet passthru subsystem.
>
> Why should we ever set REQ_NOWAIT at all? Nothing prevents the
> host(s) queue depth from exceeding the controller queue depth...
I agree... I certainly found adding a configfs attribute for this rather
off-putting. Why would the user want an option that turns on random errors?
Logan
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next prev parent reply other threads:[~2020-10-20 15:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-20 1:44 [PATCH 0/1] nvmet: allow user to set req alloc flag Chaitanya Kulkarni
2020-10-20 1:44 ` [PATCH 1/1] " Chaitanya Kulkarni
2020-10-20 8:22 ` [PATCH 0/1] " Sagi Grimberg
2020-10-20 15:39 ` Logan Gunthorpe [this message]
2020-10-20 15:53 ` Keith Busch
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