Coda File System

Re: XOR in Coda

From: Jan Harkes <>
Date: Thu, 19 Feb 2004 11:49:32 -0500
On Thu, Feb 19, 2004 at 02:00:05PM +0100, Ivan Popov wrote:
> The bandwidth of the home dsl connection is about 700 Kbyte/s
> but at 100 ms latency venus fetched files at 40-50 K/s, then when the
> provider changed the routing and the latency reduced to 45 ms, I get
> usually ~135 K/s, or, occasionally, ~300 K/s. This data is not at
> all exact, but the numbers are in that order...

That is to be expected... The rpc2 window isn't as flexible as TCP's and
pretty much aims at having between 8 and 16 packets on the wire at any
given time.

If your latency is 100ms (200ms RTT?), then an 8 packet window will give
somewhere between 40 and 80 KB/s (i.e. (8|16 * 1024) / 0.200). When the
latency drops to about 45ms, I would estimate something between 182KB/s
and 364KB/s. There is ofcourse some overhead so the numbers you give are
pretty much in the right ballpark.

> For comparison, when a client and the server are connected to the same
> 100 Mbit switch, the speed at fetching is 6.5...10 Mbyte/s.

Latency on a local area network is typically <1ms, so the window doesn't
matter all that much anymore and the network (and disc) and the fact
that we deal with the whole data streaming/retransmission stuff in
userspace become the limiting factors.

Received on 2004-02-19 11:52:23