Quoting Andy Furniss <andy.furniss@xxxxxxxxxxxxx>: > Jonathan Lynch wrote: > > This was down to the tx buffer size on the network card i was using. It > > was an Intel 82547EI gigabit Card using the e1000 driver and operating > > at 100mbit. The tx buffer was set to 256 which caused this huge delay. > > The minimum the driver lets me reduce the tx buffer size using ethtool > > is 80. By reducing the tx ring buffer to 80, the delay when there is > > full link utilisation and a maximum queue of 10 packets was reduced from > > 30ms to 10ms. > > > > The 3com 3c59x vortex driver uses a tx buffer of 16. I reduced the tx to > > 16 on the e1000 driver, but the max throughput i could achieve on the > > interface went down. > > > > Has anyone experimented with reducing the size of the tx buffer on this > > card to get a good balance between delay and throughput ? > > Strange - I thought that as long as you are under rate for the link then > the most htb should burst per tick is the burst size specified. > > That assumes one bulk class - more will make it worse. > > Andy. > Just noticed your reply there, havnt been very busy lately and havnt been checked LARTC in a while. say for example with a htb qdisc configured with a ceil of 100 Mbit (overhead 24 mpu 84 mtu 1600 burst 12k cburst 12k quantum 1500) or a queue discipline that doesnt rate limit such as prio or red there was a delay of 30 ms imposed when the outgoing interface was saturated and the tx ring size was 256. when the tx ring size was reduced to 80 the delay was around 9ms. The tx ring is a fifo structure. The NIC driver uses DMA to transmit packets from the tx ring. these are worst case delays when The tx ring is full of maximum size FTP packets with the VoIP packet at the end. The VoIP has to wait for all the FTP packets to be transmitted. When the rate was reduced to 99Mbit the maximum delay imposed is about 2ms. It seems that with the reduced rate there is time to clear more packets from the TX ring...there are less packets in the ring resulting in a lower delay. But the delay increases linearly. Also a question when defining the following parameters (overhead 24 mpu 84 mtu 1600 burst 12k cburst 12k quantum 1500) i have them defined on all classes and on the htb qdisc itself. Is there a minimum place where they can be specified...ie just on the htb qdisc itself, or do they have to be specified on all Jonathan _______________________________________________ LARTC mailing list LARTC@xxxxxxxxxxxxxxx http://mailman.ds9a.nl/cgi-bin/mailman/listinfo/lartc
