On Thu, 1 May 2008, slashdev wrote: > On Wed, Apr 30, 2008 at 11:43 PM, Bill Fink <billfink@xxxxxxxxxxxxxx> wrote: > > > > On Wed, 30 Apr 2008, slashdev wrote: > > > > > just a quick note. i turned off TSO on both ends and w/o any cable > > > swap (or switch port change), the thruput jumped from 30Mbps to > > > 60Mbps for the 20ms rtt case. not sure what would cause that. > > > > > > further, the 100 Mbps link that i've been referring to, is actually > > > composed of GigE cards at the endpoints over a 100Mbps vlan. > > > > > > just wanted to point out these two facts while i get busy fixing > > > up any potential cabling or switch problems. will also report back > > > how does cross-over cable fair in this setup... > > > > The rate mismatch from GigE down to 100 Mbps can cause serious > > performance degradation due to packet loss if there is insufficient > > buffering in the switch. Rate limiting by judicious setting of the > > window size might help (with nuttcp could also try rate limiting > > using the "-Ri90m" parameter). > > thanks for reminding me of that option :-) > > but on my setup, i get maximum thruput (without changing any cables > or switch ports) with TSO turned OFF. with it being ON, rate limiting > nuttcp does not help. the thruput stays same low at around 30Mbps. > > because i guess rate-limiting in this case is at much higher layers, > and does not prevent the card from injecting large # segments > segments on the wire (when TSO is enabled) -- causing the switch > to drop packets (due to large instantaneous incoming rate). > > does that logic make sense? Yes, it makes perfect sense. I have seen similar effects with other rate mismatch situations. And I see from your other reply that when there is no rate mismatch you were able to fill a GigE pipe as expected. -Bill -- To unsubscribe from this list: send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
