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

[Jens Axboe <axboe@kernel.dk>]

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