On 03/17/2016 02:39 AM, Ley Foon Tan wrote:
On Thu, Mar 17, 2016 at 12:25 AM, Jens Axboe <axboe@xxxxxxxxx> wrote:
On 03/16/2016 04:18 AM, Ley Foon Tan wrote:
On Wed, Mar 16, 2016 at 2:58 AM, Jens Axboe <axboe@xxxxxxxxx> wrote:
On 03/15/2016 04:20 AM, Ley Foon Tan wrote:
Hi
In the kernel v4.4 above, we can use polling mode for the NVMe data
transfer with command below:
echo 1 > /sys/block/nvme0n1/queue/io_poll
We can see NVMe throughput increase with polling mode with dd command.
Can we run fio with polling mode as well? If yes, what are the correct
fio parameters/arguments should we use?
direct=1, and use one of the sync IO engines (psync would be a good one).
And enable io_poll like you did above, then fio should be in polled mode.
--
Jens Axboe
Hi Jens
I have tried fio with direct=1 and ioengine=psync. But the results
almost the same (low throughput). Below is example command for
sequential write.
With your experiences, any clue where is the bottleneck for low
throughput (based on fio output). Note, kernel v4.4 and ARM platform.
Polled IO helps with latencies, which means that the effects are most
pronounced on smaller block size IO. You are using 128K, which is pretty far
outside the realm of "smaller block size".
That said, you do seem to have a reduction in average latency with polling.
But given the transfer size and time, percentage wise, it's not that huge.
Yes, you are right. We can see about 20% throughput gain with 4KB
block size. But, block size greater than 4KB doesn't have much
improvement.
Do you know any other fio or OS settings that can help on the NVMe
throughput? Tried set scheduler to NOOP mode doesn't help too.
Polling isn't really going to help your throughput, it'll only do that
if you are IOPS bound. If you are missing bandwidth, you probably need
to look closer at why that is.
--
Jens Axboe
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