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 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 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. For naming, maybe ->always_iowq is better as ->no_nonblock or something like that. Or perhaps get rid of the double negation and just call it ->blocking, or maybe ->no_async_support to make it clearer? > Or can we rename IORING_SETUP_NO_OFFLOAD as IORING_SETUP_SUBMIT_MAY_WAIT > and still punt ->always_iowq OPs to iowq? I think NO_OFFLOAD better explains that we'll never offload to io-wq. I would've called it NO_IOWQ, but I don't think that's understandable to users in the same way. The problem is that the user does need some knowledge of how ios are issued and completed in io_uring to fully grok what it does, which I'll put in the man pages. -- Jens Axboe
