On Fri, Nov 11, 2016 at 07:22:05PM +0100, Hannes Reinecke wrote: > Well, it's the same as with megasas and mpt3sas. Each of those have > a single MMIO register where the driver writes the address of the > command into. What exactly the hardware does in the back doesn't > really matter here; the command is in memory and the hardware can > access it as it sees fit. So from that point of view we can assume > having a submission queue to match the completion queue; > With that setup we do have a contention point on the single command > register, but that's about it. > We still should benefit from scsi-mq, though. How do we benefit from scsi-mq in this case? We still hit global cachelines like commands_outstanding in the driver, and we lost the batching done by the ctx -> hw_ctx layering for the single queue blk-mq case. We also get much less efficient merging and will not have the chance of having and I/O schedule in the near future. But back to my question from the last mail: What workload is improved by using this patch? -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
