On Wed, 2006-05-17 at 11:37 +0900, Tejun Heo wrote: > 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...... > > AFAIK, anticipatory doesn't interact very well with queued devices. Can > you try with deadline? > By using deadline, we observed the performance gain by NCQ. To avoid jitter, I record 6 "average throughput per process" results for NCQ and non-NCQ: NCQ: write :192 204 193 190 187 197 re-write :64 64 51 61 55 72 non-NCQ: write :192 188 206 201 189 200 re-write :36 37 40 39 37 41 Here we observed that NCQ has a better re-write performance than non- NCQ. But when using anticipatory, the test result is: NCQ: write: 233 re-write: 197 non-NCQ: write: 283 re-write: 332 Here we observed that anticipatory has a better performance than deadline. Especially re-write under anticipatory has much better performance than the one under deadline. So why users use deadline instead of anticipatory? Thanks, Forrest - : 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
