Re: [PATCH V8 0/8] io_uring: support sqe group and leased group kbuf

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

On Wed, Oct 30, 2024 at 11:08:16AM +0800, Ming Lei wrote:
> On Tue, Oct 29, 2024 at 08:43:39PM -0600, Jens Axboe wrote:

...

> > You could avoid the OP dependency with just a flag, if you really wanted
> > to. But I'm not sure it makes a lot of sense. And it's a hell of a lot
> 
> Yes, IO_LINK won't work for submitting multiple IOs concurrently, extra
> syscall makes application too complicated, and IO latency is increased.
> 
> > simpler than the sqe group scheme, which I'm a bit worried about as it's
> > a bit complicated in how deep it needs to go in the code. This one
> > stands alone, so I'd strongly encourage we pursue this a bit further and
> > iron out the kinks. Maybe it won't work in the end, I don't know, but it
> > seems pretty promising and it's soooo much simpler.
> 
> If buffer register and lookup are always done in ->prep(), OP dependency
> may be avoided.

Even all buffer register and lookup are done in ->prep(), OP dependency
still can't be avoided completely, such as:

1) two local buffers for sending to two sockets

2) group 1: IORING_OP_LOCAL_KBUF1 & [send(sock1), send(sock2)]  

3) group 2: IORING_OP_LOCAL_KBUF2 & [send(sock1), send(sock2)]

group 1 and group 2 needs to be linked, but inside each group, the two
sends may be submitted in parallel.


Thanks,
Ming