• Eric Dumazet's avatar
    [INET]: speedup inet (tcp/dccp) lookups · 81c3d547
    Eric Dumazet authored
    Arnaldo and I agreed it could be applied now, because I have other
    pending patches depending on this one (Thank you Arnaldo)
    (The other important patch moves skc_refcnt in a separate cache line,
    so that the SMP/NUMA performance doesnt suffer from cache line ping pongs)
    1) First some performance data :
    tcp_v4_rcv() wastes a *lot* of time in __inet_lookup_established()
    The most time critical code is :
    sk_for_each(sk, node, &head->chain) {
         if (INET_MATCH(sk, acookie, saddr, daddr, ports, dif))
             goto hit; /* You sunk my battleship! */
    The sk_for_each() does use prefetch() hints but only the begining of
    "struct sock" is prefetched.
    As INET_MATCH first comparison uses inet_sk(__sk)->daddr, wich is far
    away from the begining of "struct sock", it has to bring into CPU
    cache cold cache line. Each iteration has to use at least 2 cache
    This can be problematic if some chains are very long.
    2) The goal
    The idea I had is to change things so that INET_MATCH() may return
    FALSE in 99% of cases only using the data already in the CPU cache,
    using one cache line per iteration.
    3) Description of the patch
    Adds a new 'unsigned int skc_hash' field in 'struct sock_common',
    filling a 32 bits hole on 64 bits platform.
    struct sock_common {
    	unsigned short		skc_family;
    	volatile unsigned char	skc_state;
    	unsigned char		skc_reuse;
    	int			skc_bound_dev_if;
    	struct hlist_node	skc_node;
    	struct hlist_node	skc_bind_node;
    	atomic_t		skc_refcnt;
    +	unsigned int		skc_hash;
    	struct proto		*skc_prot;
    Store in this 32 bits field the full hash, not masked by (ehash_size -
    1) Using this full hash as the first comparison done in INET_MATCH
    permits us immediatly skip the element without touching a second cache
    line in case of a miss.
    Suppress the sk_hashent/tw_hashent fields since skc_hash (aliased to
    sk_hash and tw_hash) already contains the slot number if we mask with
    (ehash_size - 1)
    File include/net/inet_hashtables.h
    64 bits platforms :
    #define INET_MATCH(__sk, __hash, __cookie, __saddr, __daddr, __ports, __dif)\
         (((__sk)->sk_hash == (__hash))
         ((*((__u64 *)&(inet_sk(__sk)->daddr)))== (__cookie))   &&  \
         ((*((__u32 *)&(inet_sk(__sk)->dport))) == (__ports))   &&  \
         (!((__sk)->sk_bound_dev_if) || ((__sk)->sk_bound_dev_if == (__dif))))
    32bits platforms:
    #define TCP_IPV4_MATCH(__sk, __hash, __cookie, __saddr, __daddr, __ports, __dif)\
         (((__sk)->sk_hash == (__hash))                 &&  \
         (inet_sk(__sk)->daddr          == (__saddr))   &&  \
         (inet_sk(__sk)->rcv_saddr      == (__daddr))   &&  \
         (!((__sk)->sk_bound_dev_if) || ((__sk)->sk_bound_dev_if == (__dif))))
    - Adds a prefetch(head->chain.first) in 
    __inet_lookup_established()/__tcp_v4_check_established() and 
    __inet6_lookup_established()/__tcp_v6_check_established() and 
    __dccp_v4_check_established() to bring into cache the first element of the 
    list, before the {read|write}_lock(&head->lock);
    Signed-off-by: default avatarEric Dumazet <dada1@cosmosbay.com>
    Acked-by: default avatarArnaldo Carvalho de Melo <acme@ghostprotocols.net>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
inet_timewait_sock.h 6.35 KB