On Tue, Apr 25, 2023 at 07:31:10AM -0600, Jens Axboe wrote: > On 4/24/23 8:50?PM, Ming Lei wrote: > > On Mon, Apr 24, 2023 at 08:18:02PM -0600, Jens Axboe wrote: > >> On 4/24/23 8:13?PM, Ming Lei wrote: > >>> 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@xxxxxxxxx> > >>>>>>>> --- > >>>>>>>> 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? > >> > >> Yeah naming isn't that great, I can see how that's bit confusing. I'll > >> be happy to take suggestions on what would make it clearer. > > > > Except for the naming, I am also wondering why these ->always_iowq OPs > > aren't punted to iowq in case of IO_URING_F_NO_OFFLOAD, given it > > shouldn't improve performance by doing so because these OPs are supposed > > to be slow and always slept, not like others(buffered writes, ...), > > can you provide one hint about not offloading these OPs? Or is it just that > > NO_OFFLOAD needs to not offload every OPs? > > The whole point of NO_OFFLOAD is that items that would normally be > passed to io-wq are just run inline. This provides a way to reap the > benefits of batched submissions and syscall reductions. Some opcodes > will just never be async, and io-wq offloads are not very fast. Some of Yeah, seems io-wq is much slower than inline issue, maybe it needs to be looked into, and it is easy to run into io-wq for IOSQE_IO_LINK. > them can eventually be migrated to async support, if the underlying > mechanics support it. > > You'll note that none of the ->always_iowq opcodes are pollable. If True, then looks the ->always_iowq flag doesn't make a difference here because your patch clears IO_URING_F_NONBLOCK for !file_can_poll(req->file). Also almost all these ->always_iowq OPs are slow and blocked, if they are issued inline, the submission pipeline will be blocked. > NO_OFFLOAD is setup, it's pointless NOT to issue them with NONBLOCK > cleared, as you'd just get -EAGAIN and then need to call them again with > NONBLOCK cleared from the same context. My point is that these OPs are slow and slept, so inline issue won't improve performance actually for them, and punting to io-wq couldn't be worse too. On the other side, inline issue may hurt perf because submission pipeline is blocked when issuing these OPs. Thanks, Ming
