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tcp: Don't account for hash table size in tcp_hash()

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Currently tcp_hash() returns the hash bucket for a value, that is the hash
modulo the size of the hash table.  Usually it's a bit more flexible to
have hash functions return a "raw" hash value and perform the modulus in
the callers.  That allows the same hash function to be used for multiple
tables of different sizes, or to re-use the hash for other purposes.

We don't do anything like that with tcp_hash() at present, but we have some
plans to do so.  Prepare for that by making tcp_hash() and tcp_conn_hash()
return raw hash values.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2023-12-07 16:53:53 +11:00 committed by Stefano Brivio
parent 64e5459ba6
commit 5d5bb8c150
1 changed files with 10 additions and 13 deletions
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19
tcp.c
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@ -1160,18 +1160,15 @@ static int tcp_hash_match(const struct tcp_tap_conn *conn,
* @eport: Guest side endpoint port * @eport: Guest side endpoint port
* @fport: Guest side forwarding port * @fport: Guest side forwarding port
* *
* Return: hash value, already modulo size of the hash table * Return: hash value, needs to be adjusted for table size
*/ */
static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *faddr, static uint64_t tcp_hash(const struct ctx *c, const union inany_addr *faddr,
in_port_t eport, in_port_t fport) in_port_t eport, in_port_t fport)
{ {
struct siphash_state state = SIPHASH_INIT(c->hash_secret); struct siphash_state state = SIPHASH_INIT(c->hash_secret);
uint64_t hash;
inany_siphash_feed(&state, faddr); inany_siphash_feed(&state, faddr);
hash = siphash_final(&state, 20, (uint64_t)eport << 16 | fport); return siphash_final(&state, 20, (uint64_t)eport << 16 | fport);
return (unsigned int)(hash % TCP_HASH_TABLE_SIZE);
} }
/** /**
@ -1179,9 +1176,9 @@ static unsigned int tcp_hash(const struct ctx *c, const union inany_addr *faddr,
* @c: Execution context * @c: Execution context
* @conn: Connection * @conn: Connection
* *
* Return: hash value, already modulo size of the hash table * Return: hash value, needs to be adjusted for table size
*/ */
static unsigned int tcp_conn_hash(const struct ctx *c, static uint64_t tcp_conn_hash(const struct ctx *c,
const struct tcp_tap_conn *conn) const struct tcp_tap_conn *conn)
{ {
return tcp_hash(c, &conn->faddr, conn->eport, conn->fport); return tcp_hash(c, &conn->faddr, conn->eport, conn->fport);
@ -1199,7 +1196,7 @@ static inline unsigned tcp_hash_probe(const struct ctx *c,
const struct tcp_tap_conn *conn) const struct tcp_tap_conn *conn)
{ {
flow_sidx_t sidx = FLOW_SIDX(conn, TAPSIDE); flow_sidx_t sidx = FLOW_SIDX(conn, TAPSIDE);
unsigned b = tcp_conn_hash(c, conn); unsigned b = tcp_conn_hash(c, conn) % TCP_HASH_TABLE_SIZE;
/* Linear probing */ /* Linear probing */
while (!flow_sidx_eq(tc_hash[b], FLOW_SIDX_NONE) && while (!flow_sidx_eq(tc_hash[b], FLOW_SIDX_NONE) &&
@ -1242,7 +1239,7 @@ static void tcp_hash_remove(const struct ctx *c,
for (s = mod_sub(b, 1, TCP_HASH_TABLE_SIZE); for (s = mod_sub(b, 1, TCP_HASH_TABLE_SIZE);
(flow = flow_at_sidx(tc_hash[s])); (flow = flow_at_sidx(tc_hash[s]));
s = mod_sub(s, 1, TCP_HASH_TABLE_SIZE)) { s = mod_sub(s, 1, TCP_HASH_TABLE_SIZE)) {
unsigned h = tcp_conn_hash(c, &flow->tcp); unsigned h = tcp_conn_hash(c, &flow->tcp) % TCP_HASH_TABLE_SIZE;
if (!mod_between(h, s, b, TCP_HASH_TABLE_SIZE)) { if (!mod_between(h, s, b, TCP_HASH_TABLE_SIZE)) {
/* tc_hash[s] can live in tc_hash[b]'s slot */ /* tc_hash[s] can live in tc_hash[b]'s slot */
@ -1298,7 +1295,7 @@ static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c,
inany_from_af(&aany, af, faddr); inany_from_af(&aany, af, faddr);
b = tcp_hash(c, &aany, eport, fport); b = tcp_hash(c, &aany, eport, fport) % TCP_HASH_TABLE_SIZE;
while ((flow = flow_at_sidx(tc_hash[b])) && while ((flow = flow_at_sidx(tc_hash[b])) &&
!tcp_hash_match(&flow->tcp, &aany, eport, fport)) !tcp_hash_match(&flow->tcp, &aany, eport, fport))
b = mod_sub(b, 1, TCP_HASH_TABLE_SIZE); b = mod_sub(b, 1, TCP_HASH_TABLE_SIZE);