linux-kernel - [LSF/MM TOPIC] [ATTEND] scsi-mq

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Date:	Wed, 15 Jan 2014 15:05:48 -0800
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	lsf-pc@...ts.linux-foundation.org
Cc:	linux-scsi <linux-scsi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [LSF/MM TOPIC] [ATTEND] scsi-mq

Hi all,

I'd like to discuss the current state of scsi-mq prototype code.

And now that blk-mq is upstream for v3.13, exploring the remaining TODO
items towards an initial scsi-mq merge sometime before 2015 is upon us.

The benefits of scsi-mq remain unchanged:

  - Utilizes blk-mq's native per-cpu primitive + NUMA local friendly 
    queuing of pre-allocated struct request descriptor memory
  - Eliminates all fast-path memory allocations in SCSI-core + 
    optionally the underlying SCSI LLDs
  - Avoids fast-path Scsi_Host->host_lock + request_queue->queue_lock 
    accesses in submission + completion paths

These benefits have been discussed in greater detail in [1], and the
latest alpha quality code is available at [2] below.

The current TODO items include:

 - A plan for per device SCSI error handling
 - Proper scsi_device->sdev_gendev reference counting
 - Queuing fairness across multiple scsi-mq devices per host
 - Support for > 1 nr_hw_queues + conversion of qla2xxx + lpfc 
   LLDs that support native hardware multiqueue

Thank you,

--nab

References:

[1]:
[ATTEND] scsi-mq prototype discussion
http://marc.info/?l=linux-scsi&m=137358831329753&w=2

[2]:
scsi-mq WIP updated to v3.13-rc3
http://marc.info/?l=linux-scsi&m=138782535731722&w=2

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