svn commit: r323942 - head/sys/net

[Stephen Hurd]

Hans Petter Selasky wrote:
> On 09/24/17 01:46, Stephen Hurd wrote:
>> 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?

It looks like it would be more complex to do a similar thing in 
tcp_lro.c, and I'm not certain it would help much except in cases with a 
large number of streams that mostly end up not being coalesced.  Taking 
a quick look, tcp_lro_flush() would need to be modified to return an 
mbuf head and tail, then the caller would need to be responsible for 
combining them into a single mbuf chain and calling if_input().

Either that, or an mbuf tail could be passed into tcp_lro_flush(), the 
tail modified in there, and an mbuf head returned... that way it would 
work something like this:

The caller would be something like this:

m_head = m_tail = NULL;
LIST_FOREACH(le, bucket, hash_next) {
   head = tcp_lro_flush(lc, le, &m_tail);
   if (m_head == NULL)
     m_head = head;
}
if (m_head)
   if_input(m_head);

And tcp_lro_flush() would be something like this:

struct mbuf *tcp_lro_flush(struct lro_ctrl *lc, struct lro_entry *le, 
struct mbuf **tail)
{
   ...
   if (*tail)
     *tail->m_next = le->m_head;
   *tail = le->m_tail;
   ...
   return le->m_head;
}

Hrm, maybe it wouldn't be all that difficult after all.  :-)

I'll be driving across the country later this week, so I don't want to 
start poking into LRO then disappear, so if nobody else tries it out 
before then, I should take a look in a couple weeks.