• Eric Dumazet's avatar
    udp: introduce struct udp_table and multiple spinlocks · 645ca708
    Eric Dumazet authored
    
    
    UDP sockets are hashed in a 128 slots hash table.
    
    This hash table is protected by *one* rwlock.
    
    This rwlock is readlocked each time an incoming UDP message is handled.
    
    This rwlock is writelocked each time a socket must be inserted in
    hash table (bind time), or deleted from this table (close time)
    
    This is not scalable on SMP machines :
    
    1) Even in read mode, lock() and unlock() are atomic operations and
     must dirty a contended cache line, shared by all cpus.
    
    2) A writer might be starved if many readers are 'in flight'. This can
     happen on a machine with some NIC receiving many UDP messages. User
     process can be delayed a long time at socket creation/dismantle time.
    
    This patch prepares RCU migration, by introducing 'struct udp_table
    and struct udp_hslot', and using one spinlock per chain, to reduce
    contention on central rwlock.
    
    Introducing one spinlock per chain reduces latencies, for port
    randomization on heavily loaded UDP servers. This also speedup
    bindings to specific ports.
    
    udp_lib_unhash() was uninlined, becoming to big.
    
    Some cleanups were done to ease review of following patch
    (RCUification of UDP Unicast lookups)
    
    Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    645ca708