On Wed, Dec 06, 2023 at 08:37:27PM +0100, Stefano Brivio wrote: > On Mon, 4 Dec 2023 14:16:10 +1100 > David Gibson wrote: > > > We implement our hash table with pointers to the entry for each bucket (or > > NULL). However, the entries are always allocated within the flow table, > > meaning that a flow index will suffice, halving the size of the hash table. > > > > For TCP, just a flow index would be enough, but future uses will want to > > expand the hash table to cover indexing either side of a flow, so use a > > flow_sidx_t as the type for each hash bucket. > > > > Signed-off-by: David Gibson > > --- > > flow.h | 11 +++++++++++ > > tcp.c | 34 +++++++++++++++++++++++----------- > > 2 files changed, 34 insertions(+), 11 deletions(-) > > > > diff --git a/flow.h b/flow.h > > index c2a5190..959b461 100644 > > --- a/flow.h > > +++ b/flow.h > > @@ -53,6 +53,17 @@ static_assert(sizeof(flow_sidx_t) <= sizeof(uint32_t), > > > > #define FLOW_SIDX_NONE ((flow_sidx_t){ .flow = FLOW_MAX }) > > In hindsight, while reviewing the functions below: FLOW_MAX should > probably be MAX_FROM_BITS(FLOW_INDEX_BITS) - 1 instead (and those >= > comparisons would happily become >), so that we don't need to have a > "maximum" value that's also not allowed (then, strictly speaking, it's > more than the maximum). Right, either that or name the variable MAX_NUM_FLOWS or something. Eh, whatever. > > +/** > > + * flow_sidx_eq() - Test if two sidx values are equal > > + * @a, @b: sidx values > > + * > > + * Return: true iff @a and @b refer to the same side of the same flow > > + */ > > +static inline bool flow_sidx_eq(flow_sidx_t a, flow_sidx_t b) > > +{ > > + return (a.flow == b.flow) && (a.side == b.side); > > +} > > + > > union flow; > > > > void flow_table_compact(struct ctx *c, union flow *hole); > > diff --git a/tcp.c b/tcp.c > > index 09acf7f..7e438b7 100644 > > --- a/tcp.c > > +++ b/tcp.c > > @@ -574,7 +574,7 @@ static unsigned int tcp6_l2_flags_buf_used; > > #define CONN(idx) (&(FLOW(idx)->tcp)) > > > > /* Table for lookup from remote address, local port, remote port */ > > -static struct tcp_tap_conn *tc_hash[TCP_HASH_TABLE_SIZE]; > > +static flow_sidx_t tc_hash[TCP_HASH_TABLE_SIZE]; > > > > static_assert(ARRAY_SIZE(tc_hash) >= FLOW_MAX, > > "Safe linear probing requires hash table larger than connection table"); > > @@ -1197,10 +1197,13 @@ static unsigned int tcp_conn_hash(const struct ctx *c, > > static inline unsigned tcp_hash_probe(const struct ctx *c, > > const struct tcp_tap_conn *conn) > > { > > + flow_sidx_t sidx = FLOW_SIDX(conn, TAPSIDE); > > unsigned b; > > > > /* Linear probing */ > > - for (b = tcp_conn_hash(c, conn); tc_hash[b] && tc_hash[b] != conn; > > + for (b = tcp_conn_hash(c, conn); > > + !flow_sidx_eq(tc_hash[b], FLOW_SIDX_NONE) && > > Do we actually need to check for FLOW_SIDX_NONE explicitly? That is, > sidx we get as input here should never be FLOW_SIDX_NONE. Yes: we need to stop when we reach something matching @sidx *or* we hit an empty entry. Otherwise we'll never terminate if the entry isn't in there. > I wonder if it makes sense to take care of the possible "overflow" > outcome from step L4. of algorithm L you mentioned in 1/3. It > *shouldn't* because you're enforcing the minimum size of the hash > table, I wonder if it's a good idea anyway. Yeah, I wondered that too, it's probably a good idea for safety. I'll look at implementing that. > > + !flow_sidx_eq(tc_hash[b], sidx); > > b = (b + 1) % TCP_HASH_TABLE_SIZE) > > ; > > I respect the fact that this is fundamentally a for loop. :) On the > other hand: > > unsigned b = tcp_conn_hash(c, conn); > > while (!flow_sidx_eq(tc_hash[b], sidx)) > b = (b + 1) % TCP_HASH_TABLE_SIZE); > > ...would be a bit more readable? Hm, fair point. I think the while looked uglier in some earlier versions before I added the _probe() helper so it was duplicated in several places. > > > > @@ -1216,7 +1219,7 @@ static void tcp_hash_insert(const struct ctx *c, struct tcp_tap_conn *conn) > > { > > unsigned b = tcp_hash_probe(c, conn); > > > > - tc_hash[b] = conn; > > + tc_hash[b] = FLOW_SIDX(conn, TAPSIDE); > > flow_dbg(conn, "hash table insert: sock %i, bucket: %u", conn->sock, b); > > } > > > > @@ -1229,16 +1232,18 @@ static void tcp_hash_remove(const struct ctx *c, > > const struct tcp_tap_conn *conn) > > { > > unsigned b = tcp_hash_probe(c, conn), s; > > + union flow *flow = flow_at_sidx(tc_hash[b]); > > > > - if (!tc_hash[b]) > > + if (!flow) > > return; /* Redundant remove */ > > > > flow_dbg(conn, "hash table remove: sock %i, bucket: %u", conn->sock, b); > > > > /* Scan the remainder of the cluster */ > > - for (s = (b + 1) % TCP_HASH_TABLE_SIZE; tc_hash[s]; > > + for (s = (b + 1) % TCP_HASH_TABLE_SIZE; > > + (flow = flow_at_sidx(tc_hash[s])); > > s = (s + 1) % TCP_HASH_TABLE_SIZE) { > > - unsigned h = tcp_conn_hash(c, tc_hash[s]); > > + unsigned h = tcp_conn_hash(c, &flow->tcp); > > > > if (in_mod_range(h, b, s, TCP_HASH_TABLE_SIZE)) { > > /* tc_hash[s] can live in tc_hash[b]'s slot */ > > @@ -1248,7 +1253,7 @@ static void tcp_hash_remove(const struct ctx *c, > > } > > } > > > > - tc_hash[b] = NULL; > > + tc_hash[b] = FLOW_SIDX_NONE; > > } > > > > /** > > @@ -1263,10 +1268,10 @@ void tcp_tap_conn_update(const struct ctx *c, struct tcp_tap_conn *old, > > { > > unsigned b = tcp_hash_probe(c, old); > > > > - if (!tc_hash[b]) > > + if (!flow_at_sidx(tc_hash[b])) > > return; /* Not in hash table, nothing to update */ > > > > - tc_hash[b] = new; > > + tc_hash[b] = FLOW_SIDX(new, TAPSIDE); > > > > debug("TCP: hash table update: old index %u, new index %u, sock %i, " > > "bucket: %u", FLOW_IDX(old), FLOW_IDX(new), new->sock, b); > > @@ -1289,16 +1294,18 @@ static struct tcp_tap_conn *tcp_hash_lookup(const struct ctx *c, > > in_port_t eport, in_port_t fport) > > { > > union inany_addr aany; > > + union flow *flow; > > unsigned b; > > > > inany_from_af(&aany, af, faddr); > > > > for (b = tcp_hash(c, &aany, eport, fport); > > - tc_hash[b] && !tcp_hash_match(tc_hash[b], &aany, eport, fport); > > + (flow = flow_at_sidx(tc_hash[b])) > > + && !tcp_hash_match(&flow->tcp, &aany, eport, fport); > > Same as above about readability (somehow clashing with correctness). > > > b = (b + 1) % TCP_HASH_TABLE_SIZE) > > ; > > > > - return tc_hash[b]; > > + return &flow->tcp; > > } > > > > /** > > @@ -3090,6 +3097,11 @@ static void tcp_sock_refill_init(const struct ctx *c) > > */ > > int tcp_init(struct ctx *c) > > { > > + unsigned b; > > + > > + for (b = 0; b < TCP_HASH_TABLE_SIZE; b++) > > + tc_hash[b] = FLOW_SIDX_NONE; > > + > > if (c->ifi4) > > tcp_sock4_iov_init(c); > > > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson