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

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Date:   Tue, 3 Dec 2019 10:23:37 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Andrea Vai <andrea.vai@...pv.it>
Cc:     "Schmid, Carsten" <Carsten_Schmid@...tor.com>,
        Finn Thain <fthain@...egraphics.com.au>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Alan Stern <stern@...land.harvard.edu>,
        Jens Axboe <axboe@...nel.dk>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        USB list <linux-usb@...r.kernel.org>,
        SCSI development list <linux-scsi@...r.kernel.org>,
        Himanshu Madhani <himanshu.madhani@...ium.com>,
        Hannes Reinecke <hare@...e.com>,
        Omar Sandoval <osandov@...com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Hans Holmberg <Hans.Holmberg@....com>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Theodore Ts'o <tytso@....edu>
Subject: Re: AW: Slow I/O on USB media after commit
 f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6

On Fri, Nov 29, 2019 at 03:41:01PM +0100, Andrea Vai wrote:
> Il giorno ven, 29/11/2019 alle 10.35 +0800, Ming Lei ha scritto:
> > On Fri, Nov 29, 2019 at 08:57:34AM +0800, Ming Lei wrote:
> > 
> > > [...]
> > 
> > > Andrea, can you collect the following log when running the test
> > > on current new(bad) kernel?
> > > 
> > > 	/usr/share/bcc/tools/stackcount  -K blk_mq_make_request
> > 
> > Instead, please run the following trace, given insert may be
> > called from other paths, such as flush plug:
> > 
> > 	/usr/share/bcc/tools/stackcount -K t:block:block_rq_insert
> 
> Attached, for new (patched) bad kernel.
> 
> Produced by: start the trace script (with the pendrive already
> plugged), wait some seconds, run the test (1 trial, 1 GB), wait for
> the test to finish, stop the trace.
> 
> The copy took ~1700 seconds.

See the two path[1][2] of inserting request, and path[1] is triggered
4358 times, and the path[2] is triggered 5763 times.

The path[2] is expected behaviour. Not sure path [1] is correct, given
ext4_release_file() is supposed to be called when this inode is
released. That means the file is closed 4358 times during 1GB file
copying to usb storage.

Cc filesystem list.


[1] insert requests when returning to user mode from syscall

  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'
    4358

[2] insert requests from writeback wq context

  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_bio_write_page'
  b'mpage_submit_page'
  b'mpage_process_page_bufs'
  b'mpage_prepare_extent_to_map'
  b'ext4_writepages'
  b'do_writepages'
  b'__writeback_single_inode'
  b'writeback_sb_inodes'
  b'__writeback_inodes_wb'
  b'wb_writeback'
  b'wb_workfn'
  b'process_one_work'
  b'worker_thread'
  b'kthread'
  b'ret_from_fork'
    5763

Thanks,
Ming