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Subject: Re: AW: Slow I/O on USB media after commit
 f664a3cc17b7d0a2bc3b3ab96181e1029b0ec0e6
From:   Andrea Vai <andrea.vai@unipv.it>
To:     "Schmid, Carsten" <Carsten_Schmid@mentor.com>,
        Finn Thain <fthain@telegraphics.com.au>
Cc:     Ming Lei <ming.lei@redhat.com>,
        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>
Date:   Thu, 28 Nov 2019 08:46:57 +0100
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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.

Thanks,
Andrea