linux-kernel - Re: USB disk speed regression WD Elements - with bisect result 22547c4cc4fe20698a6a85a55b8788859134b8e4

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Message-ID: <Pine.LNX.4.44L0.1707261100400.1965-100000@iolanthe.rowland.org>
Date:   Wed, 26 Jul 2017 11:04:02 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Zdenek Kabelac <zkabelac@...hat.com>
cc:     Guenter Roeck <linux@...ck-us.net>,
        LKML <linux-kernel@...r.kernel.org>, <dianders@...omium.org>,
        <gregkh@...uxfoundation.org>
Subject: Re: USB disk speed regression WD Elements - with bisect result
 22547c4cc4fe20698a6a85a55b8788859134b8e4

On Wed, 26 Jul 2017, Zdenek Kabelac wrote:

> Well I do have 4.13-rc1 kernel - where the only difference is the revert
> of mentioned patched - so I can provide probably traces from this one if that
> helps anything.
> 
> What is not quite clear to me - why T440 works.
> 
> Could this be in some way related to the fact that T61 is USB2 only old lenovo 
> machine while T440 works with  USB3 (new SuperSpeed USB device number...)

Very likely that is the reason.  The hardware is different.

> So maybe there is some time-sensitive logic - where WD Elements
> decides to be USB2 or USB3 device ???

The decision has to be agreed upon on both sides -- the drive and the 
kernel.  If you enable debugging in the kernel, we'll have a better 
picture of what it is deciding to do.

Alan Stern