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authorNeilBrown <neilb@suse.com>2019-04-02 10:07:45 +1100
committerDavid S. Miller <davem@davemloft.net>2019-04-07 19:12:12 -0700
commit8f0db018006a421956965e1149234c4e8db718ee (patch)
tree40a6c226d3dc13cebf65017a23061e50007c0ef0 /net/bridge
parentff302db965b57c141297911ea647d36d11fedfbe (diff)
rhashtable: use bit_spin_locks to protect hash bucket.
This patch changes rhashtables to use a bit_spin_lock on BIT(1) of the bucket pointer to lock the hash chain for that bucket. The benefits of a bit spin_lock are: - no need to allocate a separate array of locks. - no need to have a configuration option to guide the choice of the size of this array - locking cost is often a single test-and-set in a cache line that will have to be loaded anyway. When inserting at, or removing from, the head of the chain, the unlock is free - writing the new address in the bucket head implicitly clears the lock bit. For __rhashtable_insert_fast() we ensure this always happens when adding a new key. - even when lockings costs 2 updates (lock and unlock), they are in a cacheline that needs to be read anyway. The cost of using a bit spin_lock is a little bit of code complexity, which I think is quite manageable. Bit spin_locks are sometimes inappropriate because they are not fair - if multiple CPUs repeatedly contend of the same lock, one CPU can easily be starved. This is not a credible situation with rhashtable. Multiple CPUs may want to repeatedly add or remove objects, but they will typically do so at different buckets, so they will attempt to acquire different locks. As we have more bit-locks than we previously had spinlocks (by at least a factor of two) we can expect slightly less contention to go with the slightly better cache behavior and reduced memory consumption. To enhance type checking, a new struct is introduced to represent the pointer plus lock-bit that is stored in the bucket-table. This is "struct rhash_lock_head" and is empty. A pointer to this needs to be cast to either an unsigned lock, or a "struct rhash_head *" to be useful. Variables of this type are most often called "bkt". Previously "pprev" would sometimes point to a bucket, and sometimes a ->next pointer in an rhash_head. As these are now different types, pprev is NULL when it would have pointed to the bucket. In that case, 'blk' is used, together with correct locking protocol. Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/bridge')
-rw-r--r--net/bridge/br_fdb.c1
-rw-r--r--net/bridge/br_multicast.c1
-rw-r--r--net/bridge/br_vlan.c1
-rw-r--r--net/bridge/br_vlan_tunnel.c1
4 files changed, 0 insertions, 4 deletions
diff --git a/net/bridge/br_fdb.c b/net/bridge/br_fdb.c
index 00573cc46c98..b1c91f66d79c 100644
--- a/net/bridge/br_fdb.c
+++ b/net/bridge/br_fdb.c
@@ -33,7 +33,6 @@ static const struct rhashtable_params br_fdb_rht_params = {
.key_offset = offsetof(struct net_bridge_fdb_entry, key),
.key_len = sizeof(struct net_bridge_fdb_key),
.automatic_shrinking = true,
- .locks_mul = 1,
};
static struct kmem_cache *br_fdb_cache __read_mostly;
diff --git a/net/bridge/br_multicast.c b/net/bridge/br_multicast.c
index 8d82107c6419..812560d7f7a2 100644
--- a/net/bridge/br_multicast.c
+++ b/net/bridge/br_multicast.c
@@ -44,7 +44,6 @@ static const struct rhashtable_params br_mdb_rht_params = {
.key_offset = offsetof(struct net_bridge_mdb_entry, addr),
.key_len = sizeof(struct br_ip),
.automatic_shrinking = true,
- .locks_mul = 1,
};
static void br_multicast_start_querier(struct net_bridge *br,
diff --git a/net/bridge/br_vlan.c b/net/bridge/br_vlan.c
index 96abf8feb9dc..0a02822b5667 100644
--- a/net/bridge/br_vlan.c
+++ b/net/bridge/br_vlan.c
@@ -21,7 +21,6 @@ static const struct rhashtable_params br_vlan_rht_params = {
.key_offset = offsetof(struct net_bridge_vlan, vid),
.key_len = sizeof(u16),
.nelem_hint = 3,
- .locks_mul = 1,
.max_size = VLAN_N_VID,
.obj_cmpfn = br_vlan_cmp,
.automatic_shrinking = true,
diff --git a/net/bridge/br_vlan_tunnel.c b/net/bridge/br_vlan_tunnel.c
index 6d2c4eed2dc8..758151863669 100644
--- a/net/bridge/br_vlan_tunnel.c
+++ b/net/bridge/br_vlan_tunnel.c
@@ -34,7 +34,6 @@ static const struct rhashtable_params br_vlan_tunnel_rht_params = {
.key_offset = offsetof(struct net_bridge_vlan, tinfo.tunnel_id),
.key_len = sizeof(__be64),
.nelem_hint = 3,
- .locks_mul = 1,
.obj_cmpfn = br_vlan_tunid_cmp,
.automatic_shrinking = true,
};