Re: [LSF/MM TOPIC] [ATTEND] scsi-mq

From: Sagi Grimberg
Date: Thu Jan 16 2014 - 11:30:05 EST

On 1/16/2014 1:05 AM, Nicholas A. Bellinger wrote:
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,



[ATTEND] scsi-mq prototype discussion

scsi-mq WIP updated to v3.13-rc3

I would be happy to join this discussion, I think it is also important to think about the interaction with iSCSI and LLDs.


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