On 5/30/2013 2:05 AM, Roland Dreier wrote:

On Wed, May 22, 2013 at 3:02 PM, Roland Dreier [off-list ref] wrote:

quoted

I'll try to find a kernel where tg3 works on this system so I can bisect.

So I finally was able to successfully bisect our problem with tg3
transmit timeouts with recent kernels.  Recall this was on on _some_
of our Dell R720 systems with 4X tg3 ethernet with devices like:

     tg3 0000:02:00.0: eth0: Tigon3 [partno(BCM95720) rev 5720000] (PCI
Express) MAC address 90:b1:1c:3f:46:b8
     tg3 0000:02:00.0: eth0: attached PHY is 5720C (10/100/1000Base-T
Ethernet) (WireSpeed[1], EEE[1])

The bisection came down to

     commit 298376d3e8f00147548c426959ce79efc47b669a
     Author: Tom Herbert [off-list ref]
     Date:   Mon Nov 28 08:33:30 2011

         tg3: Support for byte queue limits

         Changes to tg3 to use byte queue limits.

[...]

and each send completes in turn.

For now I can work around the issue by hacking BQL out of tg3 in our
kernel, but I guess it would be good to understand this tg3-specific
issue of sends not completing and handle that in the tg3 driver.

Thanks for the bisect and detailed analysis. I will investigate this 
further.

I have a system that reproduces this very reliably, so let me know if
there is any further logging or other info that would help understand
this further.

Is the 5720 a NIC or a LOM? If it's a NIC would it be possible to try it 
on a different system to see if the behaviour depends on the system at all?

Thanks,
   Roland