Date: Mon, 24 Jul 2017 10:41:12 -0400 (EDT)
From: Alan Stern <stern@rowland.harvard.edu>
To: Zdenek Kabelac <zkabelac@redhat.com>
cc: LKML <linux-kernel@vger.kernel.org>, <dianders@chromium.org>,
        <linux@roeck-us.net>, <gregkh@linuxfoundation.org>
Subject: Re: USB disk speed regression WD Elements - with bisect result
 22547c4cc4fe20698a6a85a55b8788859134b8e4
In-Reply-To: <0759ca4b-8f0b-1b3e-5073-19433795f325@redhat.com>
Message-ID: <Pine.LNX.4.44L0.1707241039210.1739-100000@iolanthe.rowland.org>
MIME-Version: 1.0
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On Mon, 24 Jul 2017, Zdenek Kabelac wrote:

> Hi
> 
> I've problem with my USB storage devices:  WD Elements 1TB.
> (Bus 004 Device 002: ID 1058:10a8 Western Digital Technologies, Inc. Elements 
> Portable (WDBUZG))
> 
> 
> After kernel >4.9  when disk is attached via cable it has very low speed 
> (less then 1MB/s).
> 
> It can run at full speed (>22MB/s) when the Linux kernel is fully rebooted (so 
> disk is attached during the reboot of Lenovo T61, C2D, Fedora Rawhide).
> 
> However when >4.9 kernel is running and disk is just attached it's very slow.
> 
> I've played a bisect game - and the clean result has been:
> 
> 22547c4cc4fe20698a6a85a55b8788859134b8e4
> 
> When I just revert this patch with 4.13-rc1 - it's again running with full 
> speed even when disk is attached (thus no reboot is needed for full speed).
> 
> 
> So while I've no idea what 22547c4cc4fe20698... is doing, it seems to have 
> some unpleasant side-effect on regular USB devices.
> 
> So what else is needed to get this properly working ?
> (assuming plain revert of  22547c4cc4fe20698 is unwanted).
> 
> What more info can I provide to get this storage 'normally' usable without 
> rebooting the machine.

Please post the dmesg logs showing what happens when the disk is 
first attached and operates slowly, and what happens when the disk is 
attached following a reboot and operates normally.

Alan Stern