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Subject8-CPU (SMP) #s for lockfree rtcache
Hi Dave,

Here are the SMP numbers that you had asked for. They were measured
on an 8-CPU SMP box (PIII Xeon 700 MHz processors, 1MB L2 cache
and 6GB RAM).

The test was as per your suggestion. rt_rcu is a patch that
uses RCU to do lockfree lookup of ipv4 route cache.

The basic test sends a fixed number of packets to random
destination addresses repeating every dest for 5 packets.
We tried two configurations of this test - 8-1-32 where
32 test processes simultaneosly uses 32 different
random seeds to generate different dest addreses and 8-4-8
where 8 sets, each consisting 4 processes all of whom use the same
random seed generating the same dst addresses, send packets
to the dest addresses repeating dest for every 5 packets.

With these basic tests, we measured under several other
conditions - avoid forced neighbor table garbage collection
by increasing the threshold and interval (to 31048576 and
60) and slowing the packet rate by introducing a delay of 2ms
between bursts of 5 packets.

Here are the results in terms of profile counts in
ip_route_output_key() - gc stands for neighbor table garbage
collection adjustment and u2000 stands for 2ms packet
rate delay. All measurements where done based on 2.5.3 kernel.

Test base rtrcu speedup
---- ---- ----- -------
8-1-32 2358 1655 29.8%
8-1-32-gc 4486 2176 51.4%
8-1-32-u2000 2990 1942 35.0%
8-1-32-u2000-gc 4047 2029 49.8%

8-4-8 2870 1965 31.5%
8-4-8-gc 3389 2083 38.5%
8-4-8-u2000 3459 2373 31.3%
8-4-8-u2000-gc 4686 2603 44.4%

Dipankar Sarma <>
Linux Technology Center, IBM Software Lab, Bangalore, India.
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