From: Eric Dumazet <redacted>
Date: Fri, 29 Jul 2005 19:57:35 +0200

nm -v /usr/src/linux/vmlinux | grep -5 rt_cache_stat

ffffffff804c6a80 b rover.5
ffffffff804c6a88 b last_gc.2
ffffffff804c6a90 b rover.3
ffffffff804c6a94 b equilibrium.4
ffffffff804c6a98 b ip_fallback_id.7
ffffffff804c6aa0 B rt_cache_stat
ffffffff804c6aa8 b ip_rt_max_size
ffffffff804c6aac b ip_rt_debug
ffffffff804c6ab0 b rt_deadline

So rt_cache_stat (which is a read only pointer) is in the middle of a hot cache line (some parts of it are written over and over), that 
probably ping pong between CPUS.

One cure for this would be to declare it as "__read_mostly", that
should help a lot.  But it's not the best idea, I think.

Instead, we can do away with the pointer and use DECLARE_PERCPU() and
__get_cpu_var() for rt_cache_stat.  That would emit the most efficient
code on every architecture.