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

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Date:   Thu, 28 Nov 2019 08:49:53 +1100 (AEDT)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     "Schmid, Carsten" <Carsten_Schmid@...tor.com>
cc:     Andrea Vai <andrea.vai@...pv.it>, Ming Lei <ming.lei@...hat.com>,
        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

On Wed, 27 Nov 2019, Schmid, Carsten wrote:

> > 
> > 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?

You seem to be saying we should optimize the kernel for a pathological 
use-case merely because it used to be fast before the blk-mq conversion. 
That makes no sense to me. I suppose you have information that I don't.

I assume that your employer (and the other corporations involved in this) 
have plenty of regression test results from a variety of flash hardware to 
show that the regression is real and the device is not pathological.

I'm not privy to any of that information so I will shut up and leave you 
guys to it.

-- 

> > This in itself seems unlikely to improve performance significantly. 
> > But if the flash memory came from a bad batch, perhaps it would have 
> > that effect.
> > 
> > To find out, someone may need to source another (genuine) Kingston 
> > DataTraveller device.
> >