On Gwe, 2004-05-28 at 20:04, James Tison wrote: > FTP is a __TERRIBLE__ benchmark. Remember that besides network > bandwidth, other factors that might introduce latency are things > like OS scheduling delays/timeslicing on both client and server > ends, disk I/O delays on both ends, etc; _not_to_mention_ TCP > SYN/ACK traffic, possible retransmissions, packet fragmentation > and reassembly, etc.
I must disagree. Strongly. Lets remove the bullshit first TCP SYN/ACK - sequene of 3 packets SYN / SYN|ACK / ACK at the start of the transfer. Irrelevant for larger pakets Packet fragmentation/reassembly. Linux uses TCP MTU discovery doesn't occur. Also there is no router in the middle so doesn't occur. Irrelevant Retransmissions: These are part of the link performance and tell you about the quality of the network stacks and also the variability of the link performance and re-ordering. Important real world data. The disk to disk aspect is distorting but he's using similar tests for each case. In many case disk to disk is the right way to test anyway, its what you actually do in the real world. ttcp can do similar testing without the disk layer being involved if that matters. > think that a typical LAN routing latency of 4-6 ms is a big deal, > but the more packets that get sent (and ACKed), the more _any_ > latency will hurt your final net throughput value. We're talking > about possibly thousands of packets, and nK * X ms = seconds, > at least. For TCP the cwnd will be large for a high latency link. You can play with buffer sizes here (and my guess is that this may be precisely the problem IBM's stack has, although you'd need to review traces) The trouble with ICMP based performance testing is that 1. Modern stacks will rate limit icmp replies as per RFC recommendations 2. You are measuring how fast you can stuff data down a pipe not how fast you can process stream data. That means the benchmark doesn't tell you a lot other than that you bought gigabit ethernet. Generally I don't care how fast my pipe is I care how fast I can move data over it. ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
