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

From: Andrea Vai <andrea.vai@unipv.it>
To: Ming Lei <ming.lei@redhat.com>
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>
Subject: Re: AW: Slow I/O on USB media after commit f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
Date: Thu, 28 Nov 2019 18:34:32 +0100	[thread overview]
Message-ID: <f82fd5129e3dcacae703a689be60b20a7fedadf6.camel@unipv.it> (raw)
In-Reply-To: <20191128091712.GD15549@ming.t460p>

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Il giorno gio, 28/11/2019 alle 17.17 +0800, Ming Lei ha scritto:
> On Thu, Nov 28, 2019 at 08:46:57AM +0100, Andrea Vai wrote:
> > Il giorno mer, 27/11/2019 alle 08.14 +0000, Schmid, Carsten ha
> > scritto:
> > > > 
> > > > > Then I started another set of 100 trials and let them run
> > > tonight, and
> > > > > the first 10 trials were around 1000s, then gradually
> decreased
> > > to
> > > > > ~300s, and finally settled around 200s with some trials
> below
> > > 70-80s.
> > > > > This to say, times are extremely variable and for the first
> time
> > > I
> > > > > noticed a sort of "performance increase" with time.
> > > > >
> > > > 
> > > > The sheer volume of testing (probably some terabytes by now)
> would
> > > > exercise the wear leveling algorithm in the FTL.
> > > > 
> > > But with "old kernel" the copy operation still is "fast", as far
> as
> > > i understood.
> > > If FTL (e.g. wear leveling) would slow down, we would see that
> also
> > > in
> > > the old kernel, right?
> > > 
> > > Andrea, can you confirm that the same device used with the old
> fast
> > > kernel is still fast today?
> > 
> > Yes, it is still fast. Just ran a 100 trials test and got an
> average
> > of 70 seconds with standard deviation = 6 seconds, aligned with
> the
> > past values of the same kernel.
> 
> Then can you collect trace on the old kernel via the previous
> script?
> 
> #!/bin/sh
> 
> MAJ=$1
> MIN=$2
> MAJ=$(( $MAJ << 20 ))
> DEV=$(( $MAJ | $MIN ))
> 
> /usr/share/bcc/tools/trace -t -C \
>     't:block:block_rq_issue (args->dev == '$DEV') "%s %d %d", args-
> >rwbs, args->sector, args->nr_sector' \
>     't:block:block_rq_insert (args->dev == '$DEV') "%s %d %d", args-
> >rwbs, args->sector, args->nr_sector'
> 
> Both the two trace points and bcc should be available on the old
> kernel.
> 

Trace attached. 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 73 seconds, roughly as already seen before with the fast
old kernel.

Thanks,
Andrea

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