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Commit 688ecfe6 authored by tom.leiming@gmail.com's avatar tom.leiming@gmail.com Committed by David S. Miller
Browse files

bpf: hash: use per-bucket spinlock 



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 for protecting bucket's
hlist, and per-bucket lock is just enough. This patch converts
the per-hashtable lock into per-bucket spinlock, so that
contention can be decreased a lot.

Signed-off-by: default avatarMing Lei <tom.leiming@gmail.com>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 45d8390c

kernel/bpf/hashtab.c

+32 −18
Original line number Diff line number Diff line
@@ -14,10 +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;

	raw_spinlock_t lock;

	struct bucket *buckets;

	atomic_t count;	/* number of elements in this hashtable */

	u32 n_buckets;	/* number of hash buckets */

	u32 elem_size;	/* size of each element in bytes */
@@ -79,33 +83,34 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr) 


	/* prevent zero size kmalloc and check for u32 overflow */

	if (htab->n_buckets == 0 ||

	    htab->n_buckets > U32_MAX / sizeof(struct hlist_head))

	    htab->n_buckets > U32_MAX / sizeof(struct bucket))

		goto free_htab;



	if ((u64) htab->n_buckets * sizeof(struct hlist_head) +

	if ((u64) htab->n_buckets * sizeof(struct bucket) +

	    (u64) htab->elem_size * htab->map.max_entries >=

	    U32_MAX - PAGE_SIZE)

		/* 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 +125,16 @@ 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 +237,7 @@ 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;
@@ -248,10 +259,11 @@ 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);

	raw_spin_lock_irqsave(&b->lock, flags);



	l_old = lookup_elem_raw(head, l_new->hash, key, key_size);
@@ -285,11 +297,11 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 
	} else {

		atomic_inc(&htab->count);

	}

	raw_spin_unlock_irqrestore(&htab->lock, flags);

	raw_spin_unlock_irqrestore(&b->lock, flags);



	return 0;

err:

	raw_spin_unlock_irqrestore(&htab->lock, flags);

	raw_spin_unlock_irqrestore(&b->lock, flags);

	kfree(l_new);

	return ret;

}
@@ -299,6 +311,7 @@ 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;
@@ -309,9 +322,10 @@ 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);

	raw_spin_lock_irqsave(&b->lock, flags);



	l = lookup_elem_raw(head, hash, key, key_size);
@@ -322,7 +336,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) 
		ret = 0;

	}



	raw_spin_unlock_irqrestore(&htab->lock, flags);

	raw_spin_unlock_irqrestore(&b->lock, flags);

	return ret;

}