Date: Wed, 9 Dec 1998 17:31:36 -0500 (EST) From: Andrew Gallatin <gallatin@cs.duke.edu> To: freebsd-current@FreeBSD.ORG Subject: increased UDP latencies in -current Message-ID: <13934.54777.633326.333061@grasshopper.cs.duke.edu>
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In the process of doing some Myrinet benchmarks, I noticed that UDP
latencies have increased markedly after upgrading from 2.2.5-stable to
3.0-current.
On identical machines (300Mhz PII, 440lx chipset, same memory
configuration) a kernel built from circa Jan. 18, 1998 2.2-stable
sources yields UDP small message latencies about 10% better than a
3.0-current kernel using both the netperf UDP_RR test & HBench-OS's
lat_udp. A 3.0 kernel from mid July yields slightly better results
than a recent -current, but not by much.
Tests run across the loopback interface for a 1 byte message:
RR/sec via us/msg via
OS rev netperf(1) HBench-OS(2)
--------- -------- ----------
2.2.5 15502.17 56.6806
3.0 (July 7) 13787.90 64.9367
3.0 (Dec 1) 13656.60 66.5090
(1)netperf2.1pl3, run via netperf -tUDP_RR -l60 -i 10,2 -Hlocalhost
(2)hbench: lat_udp.c,v 1.4 1997/06/27 00:33:58 abrown Exp $, run as
lat_udp 10000 localhost
Running tests between machines with real hardware (full duplex 100Mb
ethernet over the fxp interface, as well as Myrinet/Trapeze) mirrors
these differences. Larger messages (tried 1k and 8k) also mirror
these results (2.2.5 is ~10us faster). TCP latencies appear to be
nearly identical between OS revisions, as do UDP and TCP bandwidths.
Does anybody know where the increased UDP latency is coming from?
I initially thought the culprit might be no longer moving pcb's to the
head of the hash chain in in_pcblookup_hash (removed in
in_pcb.c,1.38). I tried replacing this code, but it doesn't make much
of a difference...
I suppose its not terribly important in the scheme of things, but it
would be interesting to know why things are slower.
------------------------------------------------------------------------------
Andrew Gallatin, Sr Systems Programmer http://www.cs.duke.edu/~gallatin
Duke University Email: gallatin@cs.duke.edu
Department of Computer Science Phone: (919) 660-6590
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