this patch fixes the issue with 0 reads. there seems to be a regression that is not specific to uring, regular syscall reads slowed down noticeably. On Mon, 24 Aug 2020 at 20:44, Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 8/24/20 10:18 AM, Jens Axboe wrote: > > On 8/24/20 10:13 AM, Dmitry Shulyak wrote: > >> On Mon, 24 Aug 2020 at 19:10, Jens Axboe <axboe@xxxxxxxxx> wrote: > >>> > >>> On 8/24/20 9:33 AM, Dmitry Shulyak wrote: > >>>> On Mon, 24 Aug 2020 at 17:45, Jens Axboe <axboe@xxxxxxxxx> wrote: > >>>>> > >>>>> On 8/24/20 8:06 AM, Jens Axboe wrote: > >>>>>> On 8/24/20 5:09 AM, Dmitry Shulyak wrote: > >>>>>>> library that i am using https://github.com/dshulyak/uring > >>>>>>> It requires golang 1.14, if installed, benchmark can be run with: > >>>>>>> go test ./fs -run=xx -bench=BenchmarkReadAt/uring_8 -benchtime=1000000x > >>>>>>> go test ./fs -run=xx -bench=BenchmarkReadAt/uring_5 -benchtime=8000000x > >>>>>>> > >>>>>>> note that it will setup uring instance per cpu, with shared worker pool. > >>>>>>> it will take me too much time to implement repro in c, but in general > >>>>>>> i am simply submitting multiple concurrent > >>>>>>> read requests and watching read rate. > >>>>>> > >>>>>> I'm fine with trying your Go version, but I can into a bit of trouble: > >>>>>> > >>>>>> axboe@amd ~/g/go-uring (master)> > >>>>>> go test ./fs -run=xx -bench=BenchmarkReadAt/uring_8 -benchtime=1000000x > >>>>>> # github.com/dshulyak/uring/fixed > >>>>>> fixed/allocator.go:38:48: error: incompatible type for field 2 in struct construction (cannot use type uint64 as type syscall.Iovec_len_t) > >>>>>> 38 | iovec := []syscall.Iovec{{Base: &mem[0], Len: uint64(size)}} > >>>>>> | ^ > >>>>>> FAIL github.com/dshulyak/uring/fs [build failed] > >>>>>> FAIL > >>>>>> axboe@amd ~/g/go-uring (master)> go version > >>>>>> go version go1.14.6 gccgo (Ubuntu 10.2.0-5ubuntu1~20.04) 10.2.0 linux/amd64 > >>>>> > >>>>> Alright, got it working. What device are you running this on? And am I > >>>>> correct in assuming you get short reads, or rather 0 reads? What file > >>>>> system? > >>>> > >>>> Was going to look into this. > >>>> I am getting 0 reads. This is on some old kingston ssd, ext4. > >>> > >>> I can't seem to reproduce this. I do see some cqe->res == 0 completes, > >>> but those appear to be NOPs. And they trigger at the start and end. I'll > >>> keep poking. > >> > >> Nops are used for draining and closing rings at the end of benchmarks. > >> It also appears in the beginning because of the way golang runs > >> benchmarks... > > > > OK, just checking if it was expected. > > > > But I can reproduce it now, turns out I was running XFS and that doesn't > > trigger it. With ext4, I do see zero sized read completions. I'll keep > > poking. > > Can you try with this? Looks like some cases will consume bytes from the > iterator even if they ultimately return an error. If we've consumed bytes > but need to trigger retry, ensure we revert the consumed bytes. > > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 91e2cc8414f9..609b4996a4e9 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -3152,6 +3152,8 @@ static int io_read(struct io_kiocb *req, bool force_nonblock, > } else if (ret == -EAGAIN) { > if (!force_nonblock) > goto done; > + /* some cases will consume bytes even on error returns */ > + iov_iter_revert(iter, iov_count - iov_iter_count(iter)); > ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false); > if (ret) > goto out_free; > @@ -3293,6 +3295,8 @@ static int io_write(struct io_kiocb *req, bool force_nonblock, > if (!force_nonblock || ret2 != -EAGAIN) { > kiocb_done(kiocb, ret2, cs); > } else { > + /* some cases will consume bytes even on error returns */ > + iov_iter_revert(iter, iov_count - iov_iter_count(iter)); > copy_iov: > ret = io_setup_async_rw(req, iovec, inline_vecs, iter, false); > if (!ret) > > -- > Jens Axboe >