Very poor PPP interface performance
Very poor PPP interface performance
- Subject: Very poor PPP interface performance
- From: "Jamie Wood" <email@hidden>
- Date: Tue, 26 Oct 2004 11:55:46 -0700
I have noticed that the performance of the PPP interface in Mac OS X 10.3.5
is not very good at all. I have written a simple program that brings up a
PPP interface, configures it using "ifconfig", and reads incoming packets.
If I use another program to repeatedly send UDP packets to my newly-created
PPP interface in a tight loop, the sendto() function quickly begins to
return a "No buffer space available" error. The program which is reading
packets from the PPP interface only reports that about 1% of the packets
even get through.
If I run a similar set of tests on Linux, none of the UDP packets are
dropped, and sendto returns no errors.
In another test, I tried using iperf to measure the throughput of a ssh-pppd
tunnel. The most I can get without compression enabled is 1.2 Mbits/sec over
a 10 Mbit link. The same test on Linux results in numbers which are close to
link speed (one of our tests resulted in ~28 Mbits/sec).
One interesting thing I and my collegues have observed is that if a Linux
box is used for one end of the ssh-pppd tunnel, we get about 7 Mbits/sec
download speed (Linux->Mac OS X) but only about 800 Kbits/sec upload speed
(Mac OS X->Linux).
All of this seems to indicate that there is some sort of performance problem
between the TCP stack and the PPP interface code, which is causing some sort
of serious delay when the interface picks up events from the stack.
Any information about this behavior, and suggestions for possible
workarounds/fixes would be greatly appreciated.
Thanks,
Jamie Wood
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