On Tue, Apr 25, 2023 at 05:10:41PM +0100, Pavel Begunkov wrote: > On 4/25/23 16:07, Ming Lei wrote: > > On Tue, Apr 25, 2023 at 08:50:33AM -0600, Jens Axboe wrote: > > > On 4/25/23 8:42?AM, Ming Lei wrote: > > > > 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. > > > > > > Indeed, depending on what is being linked, you may see io-wq activity > > > which is not ideal. > > > > That is why I prefer to fused command for ublk zero copy, because the > > registering buffer approach suggested by Pavel and Ziyang has to link > > register buffer OP with the actual IO OP, and it is observed that > > IOPS drops to 1/2 in 4k random io test with registered buffer approach. > > What's good about it is that you can use linked requests with it > but you _don't have to_. Can you explain it a bit? The register buffer OP has to be done before using it since the buffer register is done by calling ->uring_cmd(). > > Curiously, I just recently compared submitting 8 two-request links > (16 reqs in total) vs submit(8)+submit(8), all that in a loop. > The latter was faster. It wasn't a clean experiment, but shows > that links are not super fast and would be nice to get them better. > > For the register buf approach, I tried it out, looked good to me. > It outperforms splice requests (with a hack that removes force > iowq execution) by 5-10% with synthetic benchmark. Works better than > splice(2) for QD>=2. Let me send it out, perhaps today, so we can > figure out how it compares against ublk/fused and see the margin is. Cool! I will take a look and see if it can be used for ublk zero copy. Thanks, Ming
