Limit skb to be less than 64K with TSO

Limit skb to be less than 64K with TSO

[Alan Shih]

I am lost at the following situation:

Env:
I am writing driver + smart NIC's firmware.  The smart NIC has limited
memory. It can do checksum and TSO but with 32K max.

Problem:
SKB may be 64K in size when it reaches the driver. I cannot push all 64K to
the NIC to do checksum.  Is there a way to limit the network stack to give
me only 32K or smaller segments?  If I do checksum in the main processor, it
defeats the purpose.

TIA

Alan

Re: Limit skb to be less than 64K with TSO

[David S. Miller]

On Wed, 23 Jul 2003 11:44:46 -0700
"Feldman, Scott" <scott.feldman@intel.com> wrote:

> > I am writing driver + smart NIC's firmware.  The smart NIC 
> > has limited memory. It can do checksum and TSO but with 32K max.
> 
> Do we need a netdev->tso_max so the driver can advertise the maximum TSO
> send support by h/w?

Maybe, it's easy to implement.

Add netdev->tso_max
Add sk->sk_tso_max right after sk->sk_route_caps
When sk->sk_route_caps is set, fetch netdev->tso_max via route
and put into sk->sk_tso_max.
Replace "65535" constant in tcp_sync_mss with sk->sk_tso_max.

That shoule be it.

RE: Limit skb to be less than 64K with TSO

[Feldman, Scott]

> I am writing driver + smart NIC's firmware.  The smart NIC 
> has limited memory. It can do checksum and TSO but with 32K max.

Do we need a netdev->tso_max so the driver can advertise the maximum TSO
send support by h/w?