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

["Theodore Y. Ts'o" <tytso@mit.edu>]

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