deri@ntop.org said:

In addition if you do care about performance, I believe you're willing
to turn off packet transmission and only do packet receive. 

I don't understand what you mean by this. packet-mmap works perfectly
well on an UP|PROMISC interface with no addresses bound to it. As long
as no packets are injected through a packet socket, the tx path never
gets involved.

IRQ: Linux has far too much latency, in particular at high speeds. I'm
not the right person who can say "this is the way to go", however I
believe that we need some sort of interrupt prioritization like RTIRQ
does.

I don't think this is the problem, since small-packet performance is bad
even with a fully-polling e1000 in NAPI mode. As Robert Olsson has
demonstrated, a highly-loaded napi e1000 only generates a few hundred
interrupts per second. So the vast majority of packets recieved are
coming in without a hardware interrupt occurring at all.

Could it be that each time an hw irq _is_ generated, it causes many
packets to be lost? That's a possibility. Can you explain in more detail
how you measured the effect of interrupt latency on recieve efficiency?

Finally It would be nice to have in the standard Linux core some
packet capture improvements. It could either be based on my work or on
somebody else's work. It doesn't really matter as long as Linux gets
faster.

I agree. I think a good place to start would be reading and
understanding this thread:

http://thread.gmane.org/gmane.linux.kernel/193758

There's some disagreement for a while about where all this softirq load
is coming from. It looks like an interaction of softirqs and RCU, but
the first patch doesn't help.  Finally Olsson pointed out:

http://article.gmane.org/gmane.linux.kernel/194412

that the majority of softirq's are being run from hardirq exit. Even
with NAPI. At this point, I think, it's clear that the problem exists
regardless of rcu, and indeed, Linux is bad at doing packet-mmap RX of a
small-packet gigabit flood on both 2.4 and 2.6 (my old 2.4 measurements
earlier in this thread show this).

I'm particularly interested in trying Andrea's suggestion from
http://article.gmane.org/gmane.linux.kernel/194486 , but I won't have
the time anytime soon.

Jason