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Command queueing allows the device controller to handle requests out of order. Since it has intimate knowledge of the hardware it can order requests for maximu
by megrimlock 15y ago
Command queueing allows the device controller to handle requests out of order. Since it has intimate knowledge of the hardware it can order requests for maximum throughput.
- sliverstorm 15y agoIt's worth noting this feature is used in hard drives, and was a Big Deal when it first came out (Google "NCQ")
- justincormack 15y agoActually a USB bus doesnt know much about the hardware, but can forward multiple simultaneous (SCSI) requests and if the hardware is fast it can deal with them in whatever order it wants. If you benchmark an SSD with and without queueing you get very different speeds; with hard drives there is still a difference, although not as much. EDIT benchmarks (Intel SSD) no queuing, 4k reads: 3965 iops depth 4 , 4k reads: 16,900 iops depth 8, 4k reads: 25,700 iops depth 16, 4k reads: 32,600 iops depth 32, 4k reads: 38,800 iops The benefit decreases with larger reads, but still exists.