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Date: Sat, 26 Dec 2015 17:31:34 +0800
From: Ming Lei <tom.leiming@...il.com>
To: linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
Ming Lei <ming.lei@...onical.com>
Subject: [PATCH 3/3] bpf: hash: use per-bucket spinlock
From: Ming Lei <ming.lei@...onical.com>
Both htab_map_update_elem() and htab_map_delete_elem() can be
called from eBPF program, and they may be in kernel hot path,
so it isn't efficient to use a per-hashtable lock in this two
helpers.
The per-hashtable spinlock is used just for protecting bucket's
hlist, and per-bucket lock should be enough. This patch converts
the per-hashtable lock into per-bucket spinlock, so that contention
can be decreased a lot.
Signed-off-by: Ming Lei <ming.lei@...onical.com>
---
kernel/bpf/hashtab.c | 35 +++++++++++++++++++++++++----------
1 file changed, 25 insertions(+), 10 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index d857fcb..66bad7a 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -14,9 +14,14 @@
#include <linux/filter.h>
#include <linux/vmalloc.h>
+struct bucket {
+ struct hlist_head head;
+ raw_spinlock_t lock;
+};
+
struct bpf_htab {
struct bpf_map map;
- struct hlist_head *buckets;
+ struct bucket *buckets;
raw_spinlock_t lock;
atomic_t count; /* number of elements in this hashtable */
u32 n_buckets; /* number of hash buckets */
@@ -88,24 +93,25 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
/* make sure page count doesn't overflow */
goto free_htab;
- htab->map.pages = round_up(htab->n_buckets * sizeof(struct hlist_head) +
+ htab->map.pages = round_up(htab->n_buckets * sizeof(struct bucket) +
htab->elem_size * htab->map.max_entries,
PAGE_SIZE) >> PAGE_SHIFT;
err = -ENOMEM;
- htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct hlist_head),
+ htab->buckets = kmalloc_array(htab->n_buckets, sizeof(struct bucket),
GFP_USER | __GFP_NOWARN);
if (!htab->buckets) {
- htab->buckets = vmalloc(htab->n_buckets * sizeof(struct hlist_head));
+ htab->buckets = vmalloc(htab->n_buckets * sizeof(struct bucket));
if (!htab->buckets)
goto free_htab;
}
- for (i = 0; i < htab->n_buckets; i++)
- INIT_HLIST_HEAD(&htab->buckets[i]);
+ for (i = 0; i < htab->n_buckets; i++) {
+ INIT_HLIST_HEAD(&htab->buckets[i].head);
+ raw_spin_lock_init(&htab->buckets[i].lock);
+ }
- raw_spin_lock_init(&htab->lock);
atomic_set(&htab->count, 0);
return &htab->map;
@@ -120,11 +126,16 @@ static inline u32 htab_map_hash(const void *key, u32 key_len)
return jhash(key, key_len, 0);
}
-static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
+static inline struct bucket *__select_bucket(struct bpf_htab *htab, u32 hash)
{
return &htab->buckets[hash & (htab->n_buckets - 1)];
}
+static inline struct hlist_head *select_bucket(struct bpf_htab *htab, u32 hash)
+{
+ return &__select_bucket(htab, hash)->head;
+}
+
static struct htab_elem *lookup_elem_raw(struct hlist_head *head, u32 hash,
void *key, u32 key_size)
{
@@ -227,6 +238,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
struct htab_elem *l_new, *l_old;
struct hlist_head *head;
+ struct bucket *b;
unsigned long flags;
u32 key_size;
int ret;
@@ -248,7 +260,8 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
memcpy(l_new->key + round_up(key_size, 8), value, map->value_size);
l_new->hash = htab_map_hash(l_new->key, key_size);
- head = select_bucket(htab, l_new->hash);
+ b = __select_bucket(htab, l_new->hash);
+ head = &b->head;
/* bpf_map_update_elem() can be called in_irq() */
raw_spin_lock_irqsave(&htab->lock, flags);
@@ -299,6 +312,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
{
struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
struct hlist_head *head;
+ struct bucket *b;
struct htab_elem *l;
unsigned long flags;
u32 hash, key_size;
@@ -309,7 +323,8 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
key_size = map->key_size;
hash = htab_map_hash(key, key_size);
- head = select_bucket(htab, hash);
+ b = __select_bucket(htab, hash);
+ head = &b->head;
raw_spin_lock_irqsave(&htab->lock, flags);
--
1.9.1
--
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