Re: AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6

Theodore Y. Ts'o
2019-12-23T16:26:51Z

On Mon, Dec 23, 2019 at 09:08:28PM +0800, Ming Lei wrote:
>
> From the above trace:
>
> b'blk_mq_sched_request_inserted'
> b'blk_mq_sched_request_inserted'
> b'dd_insert_requests'
> b'blk_mq_sched_insert_requests'
> b'blk_mq_flush_plug_list'
> b'blk_flush_plug_list'
> b'io_schedule_prepare'
> b'io_schedule'
> b'rq_qos_wait'
> b'wbt_wait'
> b'__rq_qos_throttle'
> b'blk_mq_make_request'
> b'generic_make_request'
> b'submit_bio'
> b'ext4_io_submit'
> b'ext4_writepages'
> b'do_writepages'
> b'__filemap_fdatawrite_range'
> b'ext4_release_file'
> b'__fput'
> b'task_work_run'
> b'exit_to_usermode_loop'
> b'do_syscall_64'
> b'entry_SYSCALL_64_after_hwframe'
> b'cp' [19863]
> 4400
>
> So this write is clearly from 'cp' process, and it should be one
> ext4 fs issue.

We need a system call trace of the cp process, to understand what
system call is resulting in fput, (eg., I assume it's close(2) but
let's be sure), and often it's calling that system call.

What cp process is it? Is it from shellutils? Is it from busybox?

- Ted