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

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Date:   Thu, 28 Nov 2019 18:34:32 +0100
From:   Andrea Vai <andrea.vai@...pv.it>
To:     Ming Lei <ming.lei@...hat.com>
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>
Subject: Re: AW: Slow I/O on USB media after commit
 f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6

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

Download attachment "log_ming_20191128_182751.zip" of type "application/zip" (118068 bytes)