trafgen: keep a small initial ring buffer size to reduce cache-misses
Heavily reduce the initial ring buffer size for trafgen to just 196KiB,
so that we can heavily reduce the number of cache-misses related to
cache references. People can still overwrite this setting later on via
command line option for their specific architecture if they wish.
Perhaps the RX_RING should be checked as well in netsniff-ng though the
use case there is slightly different.
Before:
Performance counter stats for 'trafgen -i blub -o dummy0 -n100000000':
137,765,493,346 instructions:k # 0.82 insns per cycle
167,438,826,578 cycles:k # 0.000 GHz
59,508,315 branch-misses:k
361 context-switches:k
6 cpu-migrations:k
134,751,541 cache-misses:k # 85.019 % of all cache refs
158,495,358 cache-references:k
755 kmem:kmem_cache_alloc
15.
139458202 seconds time elapsed
After:
Performance counter stats for 'trafgen -i blub -o dummy0 -n100000000':
137,889,782,650 instructions:k # 0.92 insns per cycle
150,239,185,971 cycles:k # 0.000 GHz
71,583,573 branch-misses:k
423 context-switches:k
7 cpu-migrations:k
60,239 cache-misses:k # 0.073 % of all cache refs
82,502,468 cache-references:k
740 kmem:kmem_cache_alloc
12.
028787964 seconds time elapsed
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>