Re: Large number of empty reads on 5.9-rc2 under moderate load

[Dmitry Shulyak <yashulyak@gmail.com>]

Was going to look into this.
I am getting 0 reads. This is on some old kingston ssd, ext4.

On Mon, 24 Aug 2020 at 17:45, Jens Axboe <axboe@kernel.dk> 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?
>
> --
> Jens Axboe
>