[OLPC-devel] Network driver (?) and performance penalty

[Yoshiki Ohshima]

  Hello,

  We, the member at the Viewpoints Research Institute, are working on
the project to make Squeak environment work on OLPC.  (The "eToys
team" in
http://laptop.media.mit.edu/laptopnews.nsf/latest/news?opendocument=.
is us.)

  While taking some benchmarks, we noticed that having a USB-ethernet
adaptor connected to a USB port (either through external hub or
directly) makes things slow down, even with no data transmitted via
network.  Most easily noticable is when our application is doing
memory region copy (copy one concective memory region to another by a
routine written in ANSI-C).  It is typically 20% slower than without
network adaptor connected.  We tested it with Walter at OLPC office
last week, and the mesh network shows similar effects.

  One theory is that activity of the network driver is affecting the
CPU cache or memory bus.

  This is an interesting case because it may give us almost free 20%
speed up.  Hopefully the gurus have time to take a look at it.  Even
with 20% slowdown, Squeak looks pretty usable on OLPC.  We'll work on
the Sugar integration of it in September.

  Thank you!

-- Yoshiki