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

From: Andrea Vai <andrea.vai@unipv.it>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: Ming Lei <ming.lei@redhat.com>,
	"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: Mon, 23 Dec 2019 19:45:57 +0100	[thread overview]
Message-ID: <bb5d395fe47f033be0b8ed96cbebf8867d2416c4.camel@unipv.it> (raw)
In-Reply-To: <20191223172257.GB3282@mit.edu>

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Il giorno lun, 23/12/2019 alle 12.22 -0500, Theodore Y. Ts'o ha
scritto:
> On Mon, Dec 23, 2019 at 05:29:27PM +0100, Andrea Vai wrote:
> > I run the cp command from a bash script, or from a bash shell. I
> don't
> > know if this answer your question, otherwise feel free to tell me
> a
> > way to find the answer to give you.
> 
> What distro are you using, and/or what package is the cp command
> coming from, and what is the package name and version?

Fedora 30

$ rpm -qf `which cp`
coreutils-8.31-6.fc30.x86_64

> 
> Also, can you remind me what the bash script is and how many files
> you are copying?

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.

> 
> Can you change the script so that the cp command is prefixed by:
> 
> "strace -tTf -o /tmp/st "
> 
> e.g.,
> 
> 	strace -tTf -o /tmp/st cp <args>
> 
> And then send me
btw, please tell me if "me" means only you or I cc: all the
recipients, as usual

>  the /tmp/st file.  This will significantly change the
> time, so don't do this for measuring performance.  I just want to
> see
> what the /bin/cp command is *doing*.

I will do it, but I have a doubt. Since the problem doesn't happen
every time, is it useful to give you a trace of a "fast" run? And, if
it's not, I think I should measure performance with the trace command
prefix, to identify a "slow" run to report you. Does it make sense?

Thanks,
Andrea

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