For small random reads across the full stroke of the disk, you should see 50-80% improvement in performance, regardless of the state of read cache, at a depth of 32. For small random writes across the full stroke, performance should be unchanged if write cache is enabled in the drive. If write cache is disabled, you should see the same 50-80% performance improvement as for random reads. For sequential operations NCQ won't make much of a difference, and as the command block size increases, the performance delta will shrink between queued and non-queued. The exact asymptote is a function of many manufacturer and model-specific details. Remember that these are all ops/sec measurements. Command latency is a different kettle of fish. --eric On 10/12/06, Fajun Chen <fajunchen@xxxxxxxxx> wrote:
Hi Folks, I'm writing a program to test SATA Sil3124 NCQ feature. I assume NCQ is supported by libata by default, correct? Multi threading approach is used to send AT commands to device asynchronously. I can verify that data are sent to the device and read back correctly, but I don't know how to verify if NCQ works. Do I expect to see consistent performance gain in random read/write in NCQ mode? Thanks, Fajun - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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