Intel e1000 ethernet device, change in kernel v3.4, and jumbo frames setting DENIED.

Intel e1000 ethernet device, change in kernel v3.4, and jumbo frames setting DENIED.

[D. Stussy]

There has been some changes to the driver such that things like checksum 
verification is offloaded from the CPU.  However, this blocks the ability to 
set a jumbo frame.  The kernel does record an error indicating that checksum 
offloading need be disabled fro jumbo frame MTU sizes to be used.  My e1000 
interfaces use the 82574L chipset.

1)  Was this an intentional change?
2)  How do I disable that function so I can set jumbo frames with "ifconfig" 
or "ip"?  I simply don't know what setting I need to pass.

Exact kernel message:  "Jumbo frames cannot be enabled when both receive 
checksum offload and receive hashing are enabled.  Disable one of the receive 
offload features before enabling jumbos." 

Re: Intel e1000 ethernet device, change in kernel v3.4, and jumbo frames setting DENIED.

[Henrique de Moraes Holschuh]

On Wed, 04 Jul 2012, D. Stussy wrote:
> There has been some changes to the driver such that things like
> checksum verification is offloaded from the CPU.  However, this
> blocks the ability to set a jumbo frame.  The kernel does record an
> error indicating that checksum offloading need be disabled fro jumbo
> frame MTU sizes to be used.  My e1000 interfaces use the 82574L
> chipset.
> 
> 1)  Was this an intentional change?

Yes, but I understand Intel is trying to come up with a way not to need it.

> 2)  How do I disable that function so I can set jumbo frames with
> "ifconfig" or "ip"?  I simply don't know what setting I need to
> pass.

ethtool can do it.  Check its manpage, it can manipulate the various NIC
offload engines, as well as other parameters such as dma ring buffer size,
etc.

-- 
  "One disk to rule them all, One disk to find them. One disk to bring
  them all and in the darkness grind them. In the Land of Redmond
  where the shadows lie." -- The Silicon Valley Tarot
  Henrique Holschuh

Re: Intel e1000 ethernet device, change in kernel v3.4, and jumbo frames setting DENIED.

[D. Stussy]

"Henrique de Moraes Holschuh"  wrote in message 
news:jjGoO-7l0-19@gated-at.bofh.it...

On Wed, 04 Jul 2012, D. Stussy wrote:
> There has been some changes to the driver such that things like
> checksum verification is offloaded from the CPU.  However, this
> blocks the ability to set a jumbo frame.  The kernel does record an
> error indicating that checksum offloading need be disabled fro jumbo
> frame MTU sizes to be used.  My e1000 interfaces use the 82574L
> chipset.
>
> 1)  Was this an intentional change?

Yes, but I understand Intel is trying to come up with a way not to need it.

> 2)  How do I disable that function so I can set jumbo frames with
> "ifconfig" or "ip"?  I simply don't know what setting I need to
> pass.

ethtool can do it.  Check its manpage, it can manipulate the various NIC
offload engines, as well as other parameters such as dma ring buffer size,
etc.
=====================
I'll look into it.  Thanks. 

Re: Intel e1000 ethernet device, change in kernel v3.4, and jumbo frames setting DENIED.

[D. Stussy]

"Henrique de Moraes Holschuh"  wrote in message 
news:jjGoO-7l0-19@gated-at.bofh.it...
On Wed, 04 Jul 2012, D. Stussy wrote:
> There has been some changes to the driver such that things like
> checksum verification is offloaded from the CPU.  However, this
> blocks the ability to set a jumbo frame.  The kernel does record an
> error indicating that checksum offloading need be disabled fro jumbo
> frame MTU sizes to be used.  My e1000 interfaces use the 82574L
> chipset.
>
> 1)  Was this an intentional change?

Yes, but I understand Intel is trying to come up with a way not to need it.
==============
OK, found the modification.  NETIF_F_RXHASH turned on by default in a 
modification ("Receive Packet Steering support") from January 26, 2012.

Features which have no OFF setting should DEFAULT OFF and wait to be 
explicitly enabled.  The change which was inserted is stupid.
==============

> 2)  How do I disable that function so I can set jumbo frames with
> "ifconfig" or "ip"?  I simply don't know what setting I need to
> pass.

ethtool can do it.  Check its manpage, it can manipulate the various NIC
offload engines, as well as other parameters such as dma ring buffer size,
etc.
===============
Got it:  ethtool -K eth0 rx off

However, I'd prefer to turn off hashing instead of the checksum and I didn't 
recognize a single setting which would do that.  Under "ethtool -N", there 
seem to be 8 settings, but none of the options seemed to disable hashing 
(without simultaneously dropping packets).  I still need help:  What is the 
correct setting I need to disable this?  I don't see a simple OFF setting.

Else, this part of the patch should be reversed:
--- a/drivers/net/ethernet/intel/e1000e/netdev.c
+++ b/drivers/net/ethernet/intel/e1000e/netdev.c
@@ -6136,6 +6213,7 @@ static int __devinit e1000_probe(struct pci_dev *pdev,
NETIF_F_HW_VLAN_TX |
NETIF_F_TSO |
NETIF_F_TSO6 |
+                NETIF_F_RXHASH |
NETIF_F_RXCSUM |
NETIF_F_HW_CSUM);