• Anton Blanchard's avatar
    ipv4: Limit size of route cache hash table · c9503e0f
    Anton Blanchard authored
    Right now we have no upper limit on the size of the route cache hash table.
    On a 128GB POWER6 box it ends up as 32MB:
    
        IP route cache hash table entries: 4194304 (order: 9, 33554432 bytes)
    
    It would be nice to cap this for memory consumption reasons, but a massive
    hashtable also causes a significant spike when measuring OS jitter.
    
    With a 32MB hashtable and 4 million entries, rt_worker_func is taking
    5 ms to complete. On another system with more memory it's taking 14 ms.
    Even though rt_worker_func does call cond_sched() to limit its impact,
    in an HPC environment we want to keep all sources of OS jitter to a minimum.
    
    With the patch applied we limit the number of entries to 512k which
    can still be overriden by using the rt_entries boot option:
    
        IP route cache hash table entries: 524288 (order: 6, 4194304 bytes)
    
    With this patch rt_worker_func now takes 0.460 ms on the same system.
    Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
    Acked-by: default avatarEric Dumazet <dada1@cosmosbay.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    c9503e0f
route.c 84.1 KB