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SubjectRe: scsi-mq V2
On 06/27/14 00:07, Elliott, Robert (Server Storage) wrote:
>> -----Original Message-----
>> From: Jens Axboe []
>> Sent: Wednesday, 25 June, 2014 11:51 PM
>> To: Christoph Hellwig; James Bottomley
>> Cc: Bart Van Assche; Elliott, Robert (Server Storage); linux-
>> Subject: Re: scsi-mq V2
>> On 2014-06-25 10:51, Christoph Hellwig wrote:
>>> This is the second post of the scsi-mq series.
> ...
>>> Changes from V1:
>>> - rebased on top of the core-for-3.17 branch, most notable the
>>> scsi logging changes
>>> - fixed handling of cmd_list to prevent crashes for some heavy
>>> workloads
>>> - fixed incorrect handling of !target->can_queue
>>> - avoid scheduling a workqueue on I/O completions when no queues
>>> are congested
>>> In addition to the patches in this thread there also is a git available at:
>>> git:// scsi-mq.2
>> You can add my acked/reviewed-by to the series.
> Since March 20th (circa LSF-MM 2014) we've run many hours of tests
> with hpsa and the scsi-mq tree. We've also done a little bit of
> testing with mpt3sas and, in the last few days, scsi_debug.
> Although there are certainly more problems to find and improvements
> to be made, it's become quite stable. It's even been used on the
> boot drives of our test servers.
> For the patches in scsi-mq.2 you may add:
> Tested-by: Robert Elliott <>

Performance of scsi-mq-v2 looks even better than that of scsi-mq-v1. The
slight single-LUN regression is gone, peak IOPS with use_blk_mq=Y on my
test setup is now 3x the performance of use_blk_mq=N and latency has
been reduced further. I think this means reducing the number of context
switches did really help :-) Detailed measurement results can be found

If you want you may add to the scsi-mq-v2 patch series:

Tested-by: Bart Van Assche <>


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