zhao, forrest wrote:
On Tue, 2006-05-16 at 19:49 +0900, Tejun Heo wrote:
I don't know the workload of iozone. But NCQ shines when there are many
concurrent IOs in progress. A good real world example would be busy
file-serving web server. It generally helps if there are multiple IO
requests. If iozone is single-threaded (IO-wise), try to run multiple
copies of them and compare the results.
Also, you need to pay attention to IO schedule in use, IIRC as and cfq
are heavily optimized for single-queued devices and might not show the
best performance depending on workload. For functionality test, I
usually use deadline. It's simpler and usually doesn't get in the way,
which, BTW, may or may not translate into better performance.
Tejun,
I run iozone with 8 concurrent threads. From my understanding, NCQ
should at least provide the same throughput as non-NCQ. But the attached
test result showed that NCQ has the lower throughput compared with non-
NCQ.
The io scheduler is anticipatory.
The kernel without NCQ is 2.6.16-rc6, the kernel with NCQ is #upstream.
The current problem is that I don't know where the bottleneck is, block
I/O layer, SCSI layer, device driver layer or hardware problem......
Can you verify that /sys/bus/scsi/devices/<device>/queue_depth is
greater than 1?
Jeff
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