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udp: dynamically size hash tables at boot time

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UDP_HTABLE_SIZE was initialy defined to 128, which is a bit small for
several setups.

4000 active UDP sockets -> 32 sockets per chain in average. An
incoming frame has to lookup all sockets to find best match, so long
chains hurt latency.

Instead of a fixed size hash table that cant be perfect for every
needs, let UDP stack choose its table size at boot time like tcp/ip
route, using alloc_large_system_hash() helper

Add an optional boot parameter, uhash_entries=x so that an admin can
force a size between 256 and 65536 if needed, like thash_entries and
rhash_entries.

dmesg logs two new lines :
[    0.647039] UDP hash table entries: 512 (order: 0, 4096 bytes)
[    0.647099] UDP Lite hash table entries: 512 (order: 0, 4096 bytes)

Maximal size on 64bit arches would be 65536 slots, ie 1 MBytes for non
debugging spinlocks.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2009-10-07 00:37:59 +00:00 • committed by David S. Miller
parent 8a6dfd43d1
commit f86dcc5aa8
6 changed files with 87 additions and 36 deletions
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6
include/linux/udp.h
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@ -45,11 +45,11 @@ static inline struct udphdr *udp_hdr(const struct sk_buff *skb)
return (struct udphdr *)skb_transport_header(skb);
}
#define UDP_HTABLE_SIZE 128
#define UDP_HTABLE_SIZE_MIN (CONFIG_BASE_SMALL ? 128 : 256)
static inline int udp_hashfn(struct net *net, const unsigned num)
static inline int udp_hashfn(struct net *net, unsigned num, unsigned mask)
{
return (num + net_hash_mix(net)) & (UDP_HTABLE_SIZE - 1);
return (num + net_hash_mix(net)) & mask;
}
struct udp_sock {