Re: [PATCH NET] e1000e: Change wthresh to 1 to avoid possible Tx stalls

[David Miller <davem@davemloft.net>]

From: Jesse Brandeburg <jesse.brandeburg@intel.com>
Date: Wed, 10 Oct 2012 18:34:20 -0700

> From: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
> 
> This patch originated from Hiroaki SHIMODA but has been modified
> by Intel with some minor cleanups and additional commit log text.
> 
> Denys Fedoryshchenko and others reported Tx stalls on e1000e with
> BQL enabled.  Issue was root caused to hardware delays. They were
> introduced because some of the e1000e hardware with transmit
> writeback bursting enabled, waits until the driver does an
> explict flush OR there are WTHRESH descriptors to write back.
> 
> Sometimes the delays in question were on the order of seconds,
> causing visible lag for ssh sessions and unacceptable tx
> completion latency, especially for BQL enabled kernels.
> 
> To avoid possible Tx stalls, change WTHRESH back to 1.
> 
> The current plan is to investigate a method for re-enabling
> WTHRESH while not harming BQL, but those patches will be later
> for net-next if they work.
> 
> please enqueue for stable since v3.3 as this bug was introduced in
> commit 3f0cfa3bc11e7f00c9994e0f469cbc0e7da7b00c
> Author: Tom Herbert <therbert@google.com>
> Date:   Mon Nov 28 16:33:16 2011 +0000
> 
>     e1000e: Support for byte queue limits
> 
>     Changes to e1000e to use byte queue limits.
> 
> Reported-by: Denys Fedoryshchenko <denys@visp.net.lb>
> Tested-by: Denys Fedoryshchenko <denys@visp.net.lb>
> Signed-off-by: Hiroaki SHIMODA <shimoda.hiroaki@gmail.com>
> CC: eric.dumazet@gmail.com
> CC: therbert@google.com
> Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>

Applied and queued up for -stable, thanks.