On 05/15/2018 12:32 PM, Sitsofe Wheeler wrote:
Hello Julien,
On 15 May 2018 at 16:20, Julien Desfossez <ju@xxxxxxxxxx> wrote:
Hi,
When stracing fio running on Linux (4.13) with libaio engine, I saw that
only one request is sent in the io_submit system call regardless of the
iodepth parameter value.
To see this:
strace -f fio --name=tmp --filename=/tmp/fio --filesize=8G \
--ioengine=libaio --bs=4k --iodepth=32 --rw=randwrite \
--runtime=10 2>&1 | grep io_submit
All of the lines look like this:
io_submit(140287955259392, 1, [{pwrite, fildes=3, str="...", nbytes=4096,
offset=1035223040}]) = 1
I would have expected to see the second parameter to be 32.
By the by, did you see the warnings related to libaio in the
manual/HOWTO (http://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-ioengine
and http://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-iodepth
) regarding buffering / not setting direct=1?
Yes I did and I usually benchmark with direct=1, I just removed
parameters while doing this test.
I see that the iodepth parameter has an impact in how many requests are sent
at the beginning (in this example, I see 32 requests sent), but after that
the requests are sent one by one as soon as one completes. I understand this
is done to keep the number of "requests in flight" steady, but this is not
what I expected when setting iodepth.
So is there a way to run fio so that we can send multiple requests per
io_submit call ?
Is iodepth_batch_submit
(http://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-iodepth-batch-submit
) and following what you're looking for?
Indeed it helps !
Apparently what I am looking for is:
--iodepth=32 --iodepth_batch=32 --iodepth_batch_complete=32
Thanks !
Julien
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