Larry McVoy wrote:
A short summary is "can someone please post a test program that sources
and sinks data at the wire speed?" because apparently I'm too old and
clueless to write such a thing.
http://www.netperf.org/svn/netperf2/trunk/
:)
WRT the different speeds in each direction talking with HP-UX, perhaps there is
an interaction between the Linux TCP stack (TSO perhaps) and HP-UX's ACK
avoidance heuristics. If that is the case, tweaking tcp_deferred_ack_max with
ndd on the HP-UX system might yield different results.
I don't recall if the igelan (broadcom) driver in HP-UX attempts to auto-tune
the interrupt throttling. I do believe the iether (intel) driver in HP-UX does.
That can be altered via lanadmin -X mumble... commands.
Later (although later than a 2.6.18 kernel IIRC) e1000 drivers do try to
auto-tune the interrupt throttling and one can see oscilations when an e1000
driver is talking to an e1000 driver. I think that can only be changed via the
InterruptThrotleRate e1000 module parameter in that era of kernel - not sure if
the Intel folks have that available via ethtool on contemporary kernels now or not.
WRT the small program making a setsockopt(SO_*BUF) call going slower than the
rsh, does rsh make the setsockopt() call, or does it bend itself to the will of
the linux stack's autotuning? What happens if your small program does not make
setsockopt(SO_*BUF) calls?
Other misc observations of variable value:
*) depending on the quantity of CPU around, and the type of test one is running,
results can be better/worse depending on the CPU to which you bind the
application. Latency tends to be best when running on the same core as takes
interrupts from the NIC, bulk transfer can be better when running on a different
core, although generally better when a different core on the same chip. These
days the throughput stuff is more easily seen on 10G, but the netperf service
demand changes are still visible on 1G.
*) agreement with the observation that the small recv calls suggest that the
application is staying-up with the network. I doubt that SO_&BUF settings would
change that, but perhaps setting watermarks might (wild ass guess). The
watermarks will do nothing on HP-UX though (IIRC).
rick jones
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