svn commit: r323942 - head/sys/net

[Hans Petter Selasky]

On 09/24/17 01:46, Stephen Hurd wrote:
> Bjoern A. Zeeb wrote:
>> On 23 Sep 2017, at 6:32, Stephen Hurd wrote:
>>
>>> Bjoern A. Zeeb wrote:
>>>> On 23 Sep 2017, at 1:35, Stephen Hurd wrote:
>>>>
>>>>> Author: shurd
>>>>> Date: Sat Sep 23 01:35:14 2017
>>>>> New Revision: 323942
>>>>> URL: https://svnweb.freebsd.org/changeset/base/323942
>>>>>
>>>>> Log:
>>>>>    Chain mbufs before passing to if_input()
>>>>>
>>>>>    Build a list of mbufs to pass to if_input() after LRO. Results in
>>>>>    12% small packet forwarding rate improvement.
>>>> forwarding seems a confusing word here..
>>>
>>> The test was small (64 byte frames) received on one interface, then 
>>> sent out on a different one using the net.inet.ip.forwarding sysctl 
>>> (controlled via the gateway_enable setting in rc.conf).
>>
>> Then this makes no sense as we don’t do LRO if forwarding is enabled 
>> on the machine;
>> https://svnweb.freebsd.org/base/head/sys/netinet/tcp_lro.c?annotate=317390#l645 
>>
> 
> Basically, it changed from this:
> 
> foreach (mbuf in rx) {
>    if (lro && tcp_lro_rx(mbuf) == 0)
>      continue;
>    if_input(mbuf)
> }
> 
> To this:
> 
> prev_mbuf = first_mbuf = NULL;
> foreach (mbuf in rx) {
>    if (lro && tcp_lro_rx(mbuf) == 0)
>      continue;
>    if (prev_mbuf) {
>      prev_mbuf->m_nextpkt = mbuf;
>      prev_mbuf = mbuf;
>    }
>    else {
>      first_mbuf = prev_mbuf = mbuf;
>    }
> }
> 
> if (first_mbuf)
>    if_input(first_mbuf);
> 
> So while before it called if_input() for each separate mbuf that was not 
> LROed, it now builds a chain of mbufs that were not LROed, and makes a 
> single call to if_input() with the whole chain.  For cases like packet 
> forwarding where no packets are LROed, performance is better.
> 

Can such a similar logic be applied inside TCP LRO aswell?

--HPS