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fib_hash: embed initial hash table in fn_zone

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While looking for false sharing problems, I noticed
sizeof(struct fn_zone) was small (28 bytes) and possibly sharing a cache
line with an often written kernel structure.

Most of the time, fn_zone uses its initial hash table of 16 slots.

We can avoid the false sharing problem by embedding this initial hash
table in fn_zone itself, so that sizeof(fn_zone) > L1_CACHE_BYTES

We did a similar optimization in commit a6501e080c (Reduce memory needs
and speedup lookups)

Add a fz_revorder field to speedup fn_hash() a bit.

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 2010-10-14 20:53:04 +00:00 committed by David S. Miller
parent 7fc4463309
commit 9bef83edfb
1 changed files with 23 additions and 29 deletions
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52
net/ipv4/fib_hash.c
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@ -54,23 +54,23 @@ struct fib_node {
struct fib_alias fn_embedded_alias;
};
#define EMBEDDED_HASH_SIZE (L1_CACHE_BYTES / sizeof(struct hlist_head))
struct fn_zone {
struct fn_zone *fz_next; /* Next not empty zone */
struct hlist_head *fz_hash; /* Hash table pointer */
int fz_nent; /* Number of entries */
int fz_divisor; /* Hash divisor */
u32 fz_hashmask; /* (fz_divisor - 1) */
#define FZ_HASHMASK(fz) ((fz)->fz_hashmask)
int fz_order; /* Zone order */
__be32 fz_mask;
u8 fz_order; /* Zone order (0..32) */
u8 fz_revorder; /* 32 - fz_order */
__be32 fz_mask; /* inet_make_mask(order) */
#define FZ_MASK(fz) ((fz)->fz_mask)
};
/* NOTE. On fast computers evaluation of fz_hashmask and fz_mask
* can be cheaper than memory lookup, so that FZ_* macros are used.
*/
struct hlist_head fz_embedded_hash[EMBEDDED_HASH_SIZE];
int fz_nent; /* Number of entries */
int fz_divisor; /* Hash size (mask+1) */
};
struct fn_hash {
struct fn_zone *fn_zones[33];
@ -79,11 +79,11 @@ struct fn_hash {
static inline u32 fn_hash(__be32 key, struct fn_zone *fz)
{
u32 h = ntohl(key)>>(32 - fz->fz_order);
u32 h = ntohl(key) >> fz->fz_revorder;
h ^= (h>>20);
h ^= (h>>10);
h ^= (h>>5);
h &= FZ_HASHMASK(fz);
h &= fz->fz_hashmask;
return h;
}
@ -147,14 +147,14 @@ static void fn_rehash_zone(struct fn_zone *fz)
int old_divisor, new_divisor;
u32 new_hashmask;
old_divisor = fz->fz_divisor;
new_divisor = old_divisor = fz->fz_divisor;
switch (old_divisor) {
case 16:
new_divisor = 256;
case EMBEDDED_HASH_SIZE:
new_divisor *= EMBEDDED_HASH_SIZE;
break;
case 256:
new_divisor = 1024;
case EMBEDDED_HASH_SIZE*EMBEDDED_HASH_SIZE:
new_divisor *= (EMBEDDED_HASH_SIZE/2);
break;
default:
if ((old_divisor << 1) > FZ_MAX_DIVISOR) {
@ -184,7 +184,8 @@ static void fn_rehash_zone(struct fn_zone *fz)
fib_hash_genid++;
write_unlock_bh(&fib_hash_lock);
fz_hash_free(old_ht, old_divisor);
if (old_ht != fz->fz_embedded_hash)
fz_hash_free(old_ht, old_divisor);
}
}
@ -210,18 +211,11 @@ fn_new_zone(struct fn_hash *table, int z)
if (!fz)
return NULL;
if (z) {
fz->fz_divisor = 16;
} else {
fz->fz_divisor = 1;
}
fz->fz_hashmask = (fz->fz_divisor - 1);
fz->fz_hash = fz_hash_alloc(fz->fz_divisor);
if (!fz->fz_hash) {
kfree(fz);
return NULL;
}
fz->fz_divisor = z ? EMBEDDED_HASH_SIZE : 1;
fz->fz_hashmask = fz->fz_divisor - 1;
fz->fz_hash = fz->fz_embedded_hash;
fz->fz_order = z;
fz->fz_revorder = 32 - z;
fz->fz_mask = inet_make_mask(z);
/* Find the first not empty zone with more specific mask */