From: harish.vasudeva@amd.com
Message-ID: <CB35231B9D59D311B18600508B0EDF2F04F280E9@caexmta9.amd.com>
To: ionut@cs.columbia.edu
cc: linux-kernel@vger.kernel.org
Subject: RE: Need some help with IP/TCP Checksum Offload
Date: Fri, 22 Feb 2002 16:56:46 -0800
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i tried setting the NETIF_F_SG flag, but the stack still gives the right checksum. 

Now, i have this 1 more question. If @ all the stack does offload chksum to the hardware, how will the driver come to know about this? Is there a per packet indication from the stack asking the driver TO-DO/OR-NOT-TO-DO chksum offloading?

thanx again
HV

-----Original Message-----
From: Ion Badulescu [mailto:ionut@cs.columbia.edu]
Sent: Friday, February 22, 2002 4:01 PM
To: Vasudeva, Harish
Cc: linux-kernel@vger.kernel.org
Subject: Re: Need some help with IP/TCP Checksum Offload


On Fri, 22 Feb 2002 14:57:22 -0800, harish.vasudeva@amd.com wrote:
> 
> I am trying to offload checksum calculation to my hardware. What i am doing in my driver (kernel 2.4.6) is :
> 
> dev->features = NETIF_F_IP_CHECKSUM;
> 
> Then, in my start_xmit( ) routine, i am parsing for the right headers & when i get the IP/TCP header, i print out the checksum & it is already the right checksum. When does the OS/Protocol offload this task? Am i missing something here?

I haven't looked at this in a long time, but at the time the checksum
offloading support was introduced, the IP stack needed both NETIF_F_SG
and NETIF_F_IP_CSUM in dev->features before it would start offloading.

The idea was that cksum support without scatter-gather support is useless,
because the csum gets calculated essentially for free while copying the data
to linearize the skbuf.

Ion

-- 
  It is better to keep your mouth shut and be thought a fool,
            than to open it and remove all doubt.

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