Re: [PATCH v3 1/2] io_uring: avoid whole io_wq_work copy for requests completed inline

Jens Axboe
2020-05-28T17:03:27Z

On 5/28/20 3:15 AM, Xiaoguang Wang wrote:
> If requests can be submitted and completed inline, we don't need to
> initialize whole io_wq_work in io_init_req(), which is an expensive
> operation, add a new 'REQ_F_WORK_INITIALIZED' to control whether
> io_wq_work is initialized.
>
> I use /dev/nullb0 to evaluate performance improvement in my physical
> machine:
> modprobe null_blk nr_devices=1 completion_nsec=0
> sudo taskset -c 60 fio -name=fiotest -filename=/dev/nullb0 -iodepth=128
> -thread -rw=read -ioengine=io_uring -direct=1 -bs=4k -size=100G -numjobs=1
> -time_based -runtime=120
>
> before this patch:
> Run status group 0 (all jobs):
> READ: bw=724MiB/s (759MB/s), 724MiB/s-724MiB/s (759MB/s-759MB/s),
> io=84.8GiB (91.1GB), run=120001-120001msec
>
> With this patch:
> Run status group 0 (all jobs):
> READ: bw=761MiB/s (798MB/s), 761MiB/s-761MiB/s (798MB/s-798MB/s),
> io=89.2GiB (95.8GB), run=120001-120001msec
>
> About 5% improvement.

I think this is a big enough of a win to warrant looking closer
at this. Just a quick comment from me so far:

> @@ -2923,7 +2943,10 @@ static int io_fsync(struct io_kiocb *req, bool force_nonblock)
> {
> /* fsync always requires a blocking context */
> if (force_nonblock) {
> - req->work.func = io_fsync_finish;
> + if (!(req->flags & REQ_F_WORK_INITIALIZED))
> + init_io_work(req, io_fsync_finish);
> + else
> + req->work.func = io_fsync_finish;

This pattern is repeated enough to warrant a helper, ala:

static void io_req_init_async(req, func)
{
if (req->flags & REQ_F_WORK_INITIALIZED)
req->work.func = func;
else
init_io_work(req, func);
}

also swapped the conditions, I tend to find it easier to read without
the negation.

--
Jens Axboe