Re: [LSF/MM TOPIC] iSCSI MQ adoption via MCS discussion

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On 01/08/15 14:45, Sagi Grimberg wrote:
Actually I started with that approach, but the independent connections
under a single session (I-T-Nexus) violates the command ordering
requirement. Plus, such a solution is specific to iSER...

Hello Sagi,

Which command ordering requirement are you referring to ? The Linux storage stack does not guarantee that block layer or SCSI commands will be processed in the same order as these commands have been submitted.

However, it might be interesting to have a look at virtscsi_pick_vq(). I think the purpose of that function is to keep queueing to the same hwq as long as any commands are being executed. This approach avoids that if an application is migrated by the scheduler from one CPU to another that commands get reordered due to have been submitted to different hwq's. I don't think we already have something similar in blk-mq but this is something that could be discussed further.

(we might want to leave something for LSF ;)).

Agreed :-)

Bart.

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