Re: [PATCH 4/4] io_uring: mark opcodes that always need io-wq punt

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

On Mon, Apr 24, 2023 at 08:08:09PM -0600, Jens Axboe wrote:
> On 4/24/23 6:57?PM, Ming Lei wrote:
> > On Mon, Apr 24, 2023 at 09:24:33AM -0600, Jens Axboe wrote:
> >> On 4/24/23 1:30?AM, Ming Lei wrote:
> >>> On Thu, Apr 20, 2023 at 12:31:35PM -0600, Jens Axboe wrote:
> >>>> Add an opdef bit for them, and set it for the opcodes where we always
> >>>> need io-wq punt. With that done, exclude them from the file_can_poll()
> >>>> check in terms of whether or not we need to punt them if any of the
> >>>> NO_OFFLOAD flags are set.
> >>>>
> >>>> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> >>>> ---
> >>>>  io_uring/io_uring.c |  2 +-
> >>>>  io_uring/opdef.c    | 22 ++++++++++++++++++++--
> >>>>  io_uring/opdef.h    |  2 ++
> >>>>  3 files changed, 23 insertions(+), 3 deletions(-)
> >>>>
> >>>> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> >>>> index fee3e461e149..420cfd35ebc6 100644
> >>>> --- a/io_uring/io_uring.c
> >>>> +++ b/io_uring/io_uring.c
> >>>> @@ -1948,7 +1948,7 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
> >>>>  		return -EBADF;
> >>>>  
> >>>>  	if (issue_flags & IO_URING_F_NO_OFFLOAD &&
> >>>> -	    (!req->file || !file_can_poll(req->file)))
> >>>> +	    (!req->file || !file_can_poll(req->file) || def->always_iowq))
> >>>>  		issue_flags &= ~IO_URING_F_NONBLOCK;
> >>>
> >>> I guess the check should be !def->always_iowq?
> >>
> >> How so? Nobody that takes pollable files should/is setting
> >> ->always_iowq. If we can poll the file, we should not force inline
> >> submission. Basically the ones setting ->always_iowq always do -EAGAIN
> >> returns if nonblock == true.
> > 
> > I meant IO_URING_F_NONBLOCK is cleared here for  ->always_iowq, and
> > these OPs won't return -EAGAIN, then run in the current task context
> > directly.
> 
> Right, of IO_URING_F_NO_OFFLOAD is set, which is entirely the point of
> it :-)

But ->always_iowq isn't actually _always_ since fallocate/fsync/... are
not punted to iowq in case of IO_URING_F_NO_OFFLOAD, looks the naming of
->always_iowq is a bit confusing?


Thanks,
Ming