Commit 2b77bdde authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

inetpeer: lower false sharing effect

Profiles show false sharing in addr_compare() because refcnt/dtime
changes dirty the first inet_peer cache line, where are lying the keys
used at lookup time. If many cpus are calling inet_getpeer() and
inet_putpeer(), or need frag ids, addr_compare() is in 2nd position in
"perf top".

Before patch, my udpflood bench (16 threads) on my 2x4x2 machine :

             5784.00  9.7% csum_partial_copy_generic [kernel]
             3356.00  5.6% addr_compare              [kernel]
             2638.00  4.4% fib_table_lookup          [kernel]
             2625.00  4.4% ip_fragment               [kernel]
             1934.00  3.2% neigh_lookup              [kernel]
             1617.00  2.7% udp_sendmsg               [kernel]
             1608.00  2.7% __ip_route_output_key     [kernel]
             1480.00  2.5% __ip_append_data          [kernel]
             1396.00  2.3% kfree                     [kernel]
             1195.00  2.0% kmem_cache_free           [kernel]
             1157.00  1.9% inet_getpeer              [kernel]
             1121.00  1.9% neigh_resolve_output      [kernel]
             1012.00  1.7% dev_queue_xmit            [kernel]
# time ./udpflood.sh

real	0m44.511s
user	0m20.020s
sys	11m22.780s

# time ./udpflood.sh

real	0m44.099s
user	0m20.140s
sys	11m15.870s

After patch, no more addr_compare() in profiles :

             4171.00 10.7% csum_partial_copy_generic   [kernel]
             1787.00  4.6% fib_table_lookup            [kernel]
             1756.00  4.5% ip_fragment                 [kernel]
             1234.00  3.2% udp_sendmsg                 [kernel]
             1191.00  3.0% neigh_lookup                [kernel]
             1118.00  2.9% __ip_append_data            [kernel]
             1022.00  2.6% kfree                       [kernel]
              993.00  2.5% __ip_route_output_key       [kernel]
              841.00  2.2% neigh_resolve_output        [kernel]
              816.00  2.1% kmem_cache_free             [kernel]
              658.00  1.7% ia32_sysenter_target        [kernel]
              632.00  1.6% kmem_cache_alloc_node       [kernel]

# time ./udpflood.sh

real	0m41.587s
user	0m19.190s
sys	10m36.370s

# time ./udpflood.sh

real	0m41.486s
user	0m19.290s
sys	10m33.650s
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 1a7a1032
......@@ -32,12 +32,17 @@ struct inet_peer {
struct inet_peer __rcu *avl_left, *avl_right;
struct inetpeer_addr daddr;
__u32 avl_height;
__u32 dtime; /* the time of last use of not
* referenced entries */
atomic_t refcnt;
u32 metrics[RTAX_MAX];
u32 rate_tokens; /* rate limiting for ICMP */
unsigned long rate_last;
unsigned long pmtu_expires;
u32 pmtu_orig;
u32 pmtu_learned;
struct inetpeer_addr_base redirect_learned;
/*
* Once inet_peer is queued for deletion (refcnt == -1), following fields
* are not available: rid, ip_id_count, tcp_ts, tcp_ts_stamp, metrics
* are not available: rid, ip_id_count, tcp_ts, tcp_ts_stamp
* We can share memory with rcu_head to help keep inet_peer small.
*/
union {
......@@ -46,17 +51,14 @@ struct inet_peer {
atomic_t ip_id_count; /* IP ID for the next packet */
__u32 tcp_ts;
__u32 tcp_ts_stamp;
u32 metrics[RTAX_MAX];
u32 rate_tokens; /* rate limiting for ICMP */
unsigned long rate_last;
unsigned long pmtu_expires;
u32 pmtu_orig;
u32 pmtu_learned;
struct inetpeer_addr_base redirect_learned;
};
struct rcu_head rcu;
struct inet_peer *gc_next;
};
/* following fields might be frequently dirtied */
__u32 dtime; /* the time of last use of not referenced entries */
atomic_t refcnt;
};
void inet_initpeers(void) __init;
......
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