Re: [PATCH 0/4] io_uring: add IORING_OP_READ[WRITE]_SPLICE_BUF

[Ming Lei <ming.lei@redhat.com>]

On Fri, Feb 10, 2023 at 02:54:29PM -0700, Jens Axboe wrote:
> On 2/10/23 8:32 AM, Ming Lei wrote:
> > Hello,
> > 
> > Add two OPs which buffer is retrieved via kernel splice for supporting
> > fuse/ublk zero copy.
> > 
> > The 1st patch enhances direct pipe & splice for moving pages in kernel,
> > so that the two added OPs won't be misused, and avoid potential security
> > hole.
> > 
> > The 2nd patch allows splice_direct_to_actor() caller to ignore signal
> > if the actor won't block and can be done in bound time.
> > 
> > The 3rd patch add the two OPs.
> > 
> > The 4th patch implements ublk's ->splice_read() for supporting
> > zero copy.
> > 
> > ublksrv(userspace):
> > 
> > https://github.com/ming1/ubdsrv/commits/io_uring_splice_buf
> >     
> > So far, only loop/null target implements zero copy in above branch:
> >     
> > 	ublk add -t loop -f $file -z
> > 	ublk add -t none -z
> > 
> > Basic FS/IO function is verified, mount/kernel building & fio
> > works fine, and big chunk IO(BS: 64k/512k) performance gets improved
> > obviously.
> 
> Do you have any performance numbers?

Simple test on ublk-loop over image in btrfs shows the improvement is
100% ~ 200%.

> Also curious on liburing regression
> tests, would be nice to see as it helps with review.

It isn't easy since it requires ublk device so far, it looks like
read to/write from one device buffer.

Thanks,
Ming