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From: Andrea Vai <andrea.vai@unipv.it>
To: Ming Lei <ming.lei@redhat.com>, "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: "Schmid, Carsten" <Carsten_Schmid@mentor.com>,
	Finn Thain <fthain@telegraphics.com.au>,
	Damien Le Moal <Damien.LeMoal@wdc.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Jens Axboe <axboe@kernel.dk>,
	Johannes Thumshirn <jthumshirn@suse.de>,
	USB list <linux-usb@vger.kernel.org>,
	SCSI development list <linux-scsi@vger.kernel.org>,
	Himanshu Madhani <himanshu.madhani@cavium.com>,
	Hannes Reinecke <hare@suse.com>, Omar Sandoval <osandov@fb.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Hans Holmberg <Hans.Holmberg@wdc.com>,
	Kernel development list <linux-kernel@vger.kernel.org>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
Date: Tue, 24 Dec 2019 07:49:37 +0100
Message-ID: <e3dc2a3e0221c0a0beb91172ba2bff1f6acc0cb7.camel@unipv.it> (raw)
In-Reply-To: <20191224012707.GA13083@ming.t460p>

Il giorno mar, 24/12/2019 alle 09.27 +0800, Ming Lei ha scritto:
> Hi Ted,
> 
> On Mon, Dec 23, 2019 at 02:53:01PM -0500, Theodore Y. Ts'o wrote:
> > On Mon, Dec 23, 2019 at 07:45:57PM +0100, Andrea Vai wrote:
> > > basically, it's:
> > > 
> > >   mount UUID=$uuid /mnt/pendrive
> > >   SECONDS=0
> > >   cp $testfile /mnt/pendrive
> > >   umount /mnt/pendrive
> > >   tempo=$SECONDS
> > > 
> > > and it copies one file only. Anyway, you can find the whole
> script
> > > attached.
> > 
> > OK, so whether we are doing the writeback at the end of cp, or
> when
> > you do the umount, it's probably not going to make any
> difference.  We
> > can get rid of the stack trace in question by changing the script
> to
> > be basically:
> > 
> > mount UUID=$uuid /mnt/pendrive
> > SECONDS=0
> > rm -f /mnt/pendrive/$testfile
> > cp $testfile /mnt/pendrive
> > umount /mnt/pendrive
> > tempo=$SECONDS
> > 
> > I predict if you do that, you'll see that all of the time is spent
> in
> > the umount, when we are trying to write back the file.
> > 
> > I really don't think then this is a file system problem at
> all.  It's
> > just that USB I/O is slow, for whatever reason.  We'll see a stack
> > trace in the writeback code waiting for the I/O to be completed,
> but
> > that doesn't mean that the root cause is in the writeback code or
> in
> > the file system which is triggering the writeback.
> 
> Wrt. the slow write on this usb storage, it is caused by two
> writeback
> path, one is the writeback wq, another is from ext4_release_file()
> which
> is triggered from exit_to_usermode_loop().
> 
> When the two write path is run concurrently, the sequential write
> order
> is broken, then write performance drops much on this particular usb
> storage.
> 
> The ext4_release_file() should be run from read() or write() syscall
> if
> Fedora 30's 'cp' is implemented correctly. IMO, it isn't expected
> behavior
> for ext4_release_file() to be run thousands of times when just
> running 'cp' once, see comment of ext4_release_file():
> 
> 	/*
> 	 * Called when an inode is released. Note that this is
> different
> 	 * from ext4_file_open: open gets called at every open, but
> release
> 	 * gets called only when /all/ the files are closed.
> 	 */
> 	static int ext4_release_file(struct inode *inode, struct file
> *filp)
> 
> > 
> > I suspect the next step is use a blktrace, to see what kind of I/O
> is
> > being sent to the USB drive, and how long it takes for the I/O to
> > complete.  You might also try to capture the output of "iostat -x
> 1"
> > while the script is running, and see what the difference might be
> > between a kernel version that has the problem and one that
> doesn't,
> > and see if that gives us a clue.
> 
> That isn't necessary, given we have concluded that the bad write
> performance is caused by broken write order.
> 
> > 
> > > > And then send me
> > > btw, please tell me if "me" means only you or I cc: all the
> > > recipients, as usual
> > 
> > Well, I don't think we know what the root cause is.  Ming is
> focusing
> > on that stack trace, but I think it's a red herring.....  And if
> it's
> > not a file system problem, then other people will be best suited
> to
> > debug the issue.
> 
> So far, the reason points to the extra writeback path from
> exit_to_usermode_loop().
> If it is not from close() syscall, the issue should be related with
> file reference
> count. If it is from close() syscall, the issue might be in 'cp''s
> implementation.
> 
> Andrea, please collect the following log or the strace log requested
> by Ted, then
> we can confirm if the extra writeback is from close() or
> read/write() syscall:
> 
> # pass PID of 'cp' to this script
> #!/bin/sh
> PID=$1
> /usr/share/bcc/tools/trace -P $PID  -t -C \
>     't:block:block_rq_insert "%s %d %d", args->rwbs, args->sector,
> args->nr_sector' \
>     't:syscalls:sys_exit_close ' \
>     't:syscalls:sys_exit_read ' \
>     't:syscalls:sys_exit_write '

Sorry if I am a bit confused, should I run it on ext4 or xfs, or
doesn't matter? What if I get it on a "fast" run? Should I throw it
away and try again until I get a slow one, or it doesn't matter?

Thanks,
Andrea


  reply index

Thread overview: 102+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <307581a490b610c3025ee80f79a465a89d68ed19.camel@unipv.it>
2019-08-20 17:13 ` Alan Stern
2019-08-23 10:39   ` Andrea Vai
2019-08-23 20:42     ` Alan Stern
2019-08-26  6:09       ` Andrea Vai
2019-08-26 16:33         ` Alan Stern
2019-09-18 15:25           ` Andrea Vai
2019-09-18 16:30             ` Alan Stern
2019-09-19  7:33               ` Andrea Vai
2019-09-19 17:54                 ` Alan Stern
2019-09-20  7:25                   ` Andrea Vai
2019-09-20  7:44                     ` Greg KH
2019-09-19  8:26               ` Damien Le Moal
2019-09-19  8:55                 ` Ming Lei
2019-09-19  9:09                   ` Damien Le Moal
2019-09-19  9:21                     ` Ming Lei
2019-09-19 14:01                 ` Alan Stern
2019-09-19 14:14                   ` Damien Le Moal
2019-09-20  7:03                     ` Andrea Vai
2019-09-25 19:30                       ` Alan Stern
2019-09-25 19:36                         ` Jens Axboe
2019-09-27 15:47                           ` Andrea Vai
2019-11-04 16:00                             ` Andrea Vai
2019-11-04 18:20                               ` Alan Stern
2019-11-05 11:48                                 ` Andrea Vai
2019-11-05 18:31                                   ` Alan Stern
2019-11-05 23:29                                     ` Jens Axboe
2019-11-06 16:03                                       ` Alan Stern
2019-11-06 22:13                                         ` Damien Le Moal
2019-11-07  7:04                                           ` Andrea Vai
2019-11-07  7:54                                             ` Damien Le Moal
2019-11-07 18:59                                               ` Andrea Vai
2019-11-08  8:42                                                 ` Damien Le Moal
2019-11-08 14:33                                                   ` Jens Axboe
2019-11-11 10:46                                                     ` Andrea Vai
2019-11-09 10:09                                                   ` Ming Lei
2019-11-09 22:28                                                 ` Ming Lei
2019-11-11 10:50                                                   ` Andrea Vai
2019-11-11 11:05                                                     ` Ming Lei
2019-11-11 11:13                                                       ` Andrea Vai
2019-11-22 19:16                                                   ` Andrea Vai
2019-11-23  7:28                                                     ` Ming Lei
2019-11-23 15:44                                                       ` Andrea Vai
2019-11-25  3:54                                                         ` Ming Lei
2019-11-25 10:11                                                           ` Andrea Vai
2019-11-25 10:29                                                             ` Ming Lei
2019-11-25 14:58                                                               ` Andrea Vai
2019-11-25 15:15                                                                 ` Ming Lei
2019-11-25 18:51                                                                   ` Andrea Vai
2019-11-26  2:32                                                                     ` Ming Lei
2019-11-26  7:46                                                                       ` Andrea Vai
2019-11-26  9:15                                                                         ` Ming Lei
2019-11-26 10:24                                                                           ` Ming Lei
2019-11-26 11:14                                                                           ` Andrea Vai
2019-11-27  2:05                                                                             ` Ming Lei
2019-11-27  9:39                                                                               ` Andrea Vai
2019-11-27 13:08                                                                                 ` Ming Lei
2019-11-27 15:01                                                                                   ` Andrea Vai
2019-11-27  0:21                                                                         ` Finn Thain
2019-11-27  8:14                                                                           ` AW: " Schmid, Carsten
2019-11-27 21:49                                                                             ` Finn Thain
2019-11-28  7:46                                                                             ` Andrea Vai
2019-11-28  8:12                                                                               ` AW: " Schmid, Carsten
2019-11-28 11:40                                                                                 ` Andrea Vai
2019-11-28 17:39                                                                                 ` Alan Stern
2019-11-28  9:17                                                                               ` Ming Lei
2019-11-28 17:34                                                                                 ` Andrea Vai
2019-11-29  0:57                                                                                   ` Ming Lei
2019-11-29  2:35                                                                                     ` Ming Lei
2019-11-29 14:41                                                                                       ` Andrea Vai
2019-12-03  2:23                                                                                         ` Ming Lei
2019-12-10  7:35                                                                                           ` Andrea Vai
2019-12-10  8:05                                                                                             ` Ming Lei
2019-12-11  2:41                                                                                               ` Theodore Y. Ts'o
2019-12-11  4:00                                                                                                 ` Ming Lei
2019-12-11 16:07                                                                                                   ` Theodore Y. Ts'o
2019-12-11 21:33                                                                                                     ` Ming Lei
2019-12-12  7:34                                                                                                       ` Andrea Vai
2019-12-18  8:25                                                                                                       ` Andrea Vai
2019-12-18  9:48                                                                                                         ` Ming Lei
     [not found]                                                                                                           ` <b1b6a0e9d690ecd9432025acd2db4ac09f834040.camel@unipv.it>
2019-12-23 13:08                                                                                                             ` Ming Lei
2019-12-23 14:02                                                                                                               ` Andrea Vai
2019-12-24  1:32                                                                                                                 ` Ming Lei
2019-12-24  8:04                                                                                                                   ` Andrea Vai
2019-12-24  8:47                                                                                                                     ` Ming Lei
2019-12-23 16:26                                                                                                               ` Theodore Y. Ts'o
2019-12-23 16:29                                                                                                                 ` Andrea Vai
2019-12-23 17:22                                                                                                                   ` Theodore Y. Ts'o
2019-12-23 18:45                                                                                                                     ` Andrea Vai
2019-12-23 19:53                                                                                                                       ` Theodore Y. Ts'o
2019-12-24  1:27                                                                                                                         ` Ming Lei
2019-12-24  6:49                                                                                                                           ` Andrea Vai [this message]
2019-12-24  8:51                                                                                                                           ` Andrea Vai
2019-12-24  9:35                                                                                                                             ` Ming Lei
2019-12-25  5:17                                                                                                                           ` Theodore Y. Ts'o
2019-12-26  2:27                                                                                                                             ` Ming Lei
2019-12-26  3:30                                                                                                                               ` Theodore Y. Ts'o
2019-12-26  8:37                                                                                                                                 ` Ming Lei
2020-01-07  7:51                                                                                                                                   ` Andrea Vai
     [not found]                                                                                                                                 ` <20200101074310.10904-1-hdanton@sina.com>
2020-01-01 13:53                                                                                                                                   ` slow IO on USB media Ming Lei
2019-11-29 11:44                                                                                     ` AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6 Bernd Schubert
2019-12-02  7:01                                                                                       ` Andrea Vai
2019-11-28 17:10                                                                           ` Andrea Vai

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