Re: [Question] How to perform stride access?

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On 2014-09-24 15:22, Sitsofe Wheeler wrote:
(Adding Jens to the CC list)

On 24 September 2014 10:52, Sitsofe Wheeler <sitsofe@xxxxxxxxx> wrote:
On 24 September 2014 09:35, Akira Hayakawa <ruby.wktk@xxxxxxxxx> wrote:

However, I [...] think I still have a problem.

I modified the command

From:
fio --name=test --filename=#{dev.path} --rw=write --ioengine=libaio --direct=1 --io_limit=32M --size=100% --ba=4k --bs=512
To:
fio --name=test --filename=#{dev.path} --rw=write:4k --ioengine=libaio --direct=1 --io_limit=32M --bs=512

The result is the runtime is too short.

This looks like a bug. I can reproduce it with 2.1.11-11-gb7f5 too:

dd if=/dev/zero of=/dev/shm/1M bs=1M count=1
fio --bs=4k --rw=write:4k --filename=/dev/shm/1M --stonewall --name=1M
--io_limit=1M  --name=2M --io_limit=2M
[...]

Run status group 0 (all jobs):
   WRITE: io=512KB, aggrb=256000KB/s, minb=256000KB/s, maxb=256000KB/s,
mint=2msec, maxt=2msec

Run status group 1 (all jobs):
   WRITE: io=512KB, aggrb=256000KB/s, minb=256000KB/s, maxb=256000KB/s,
mint=2msec, maxt=2msec

Why isn't io 1024KB for group 0? Additionally, shouldn't the total io
written each group be different? Jens?

You are doing a sequential workload, skipping 4k every time. First write will be to offset 0, next to 8KB, etc. Write 128 would be to 1040384, which is 1MB - 8KB. Hence the next feasible offset after that would be 1MB, which is end of the file. So how could it do more than 512KB of IO? That's 128 * 4KB.

I didn't read the whole thread in detail, just looked at your last example here. And for that one, I don't see anything wrong.

--
Jens Axboe

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