Re: packet size vs inter-packet gap

[Lennert Buytenhek <buytenh@xxxxxxxxxxxxxx>]

(cc'ing netdev and e1000-devel)


On Thu, Nov 25, 2004 at 11:49:45PM -0500, jamal wrote:

> Would be nice to see what happens when you kick the DMA only after
> filling up the ring.

Just to 'confirm' what you've been seeing, even this tiny little patch:

diff -urN e1000.orig/e1000_main.c e1000/e1000_main.c
--- e1000.orig/e1000_main.c     2004-11-24 15:35:23.000000000 +0100
+++ e1000/e1000_main.c  2004-11-27 22:57:08.429782838 +0100
@@ -1720,7 +1735,9 @@
        wmb();
 
        tx_ring->next_to_use = i;
+       if ((i % 4) == 0) {
        E1000_WRITE_REG(&adapter->hw, TDT, i);
+       }
 }


changes my 60B TX rate numbers from:
  612597pps
  612447pps
  612381pps
  612568pps
  612579pps

to:
  614158pps
  614179pps 
  614186pps
  614169pps
  614171pps
  614150pps
  614180pps
  614163pps
  614179pps

(As before, 32/66, 82541PI, SMP Xeon 2.4, 2.6.9-something.)  'tis not
much but definitely makes _some_ difference.


cheers,
Lennert