Commit 5e711259 authored by David S. Miller's avatar David S. Miller
Browse files

Merge branch 'bpf_hash-locking' 



Ming Lei says:

====================
bpf: hash: use per-bucket spinlock

This patchset tries to optimize ebpf hash map, and follows
the idea:

        Both htab_map_update_elem() and htab_map_delete_elem()
        can be called from eBPF program, and they may be in kernel
        hot path, it isn't efficient to use a per-hashtable lock
        in this two helpers, so this patch converts the lock into
        per-bucket spinlock.

With this patchset, looks the performance penalty from eBPF
decreased a lot, see the following test:

        1) run 'tools/biolatency' of bcc before running block test;

        2) run fio to test block throught over /dev/nullb0,
        (randread, 16jobs, libaio, 4k bs) and the test box
        is one 24cores(dual sockets) VM server:
        - without patchset:  607K IOPS
        - with this patchset: 1184K IOPS
        - without running eBPF prog: 1492K IOPS

TODO:
        - remove the per-hashtable atomic counter

V2:
        - fix checking on buckets size
V1:
        - fix the wrong 3/3 patch
====================

Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parents 26a4d063 688ecfe6

kernel/bpf/hashtab.c

+38 −26
Original line number Diff line number Diff line
@@ -14,11 +14,15 @@ 
#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;

	u32 count;	/* number of elements in this hashtable */

	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 */

};
@@ -79,34 +83,35 @@ 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);

	htab->count = 0;

	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;
@@ -248,15 +259,15 @@ 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);

	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);



	head = select_bucket(htab, l_new->hash);

	raw_spin_lock_irqsave(&b->lock, flags);



	l_old = lookup_elem_raw(head, l_new->hash, key, key_size);



	if (!l_old && unlikely(htab->count >= map->max_entries)) {

	if (!l_old && unlikely(atomic_read(&htab->count) >= map->max_entries)) {

		/* if elem with this 'key' doesn't exist and we've reached

		 * max_entries limit, fail insertion of new elem

		 */
@@ -284,13 +295,13 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value, 
		hlist_del_rcu(&l_old->hash_node);

		kfree_rcu(l_old, rcu);

	} else {

		htab->count++;

		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;

}
@@ -300,6 +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;
@@ -310,21 +322,21 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key) 
	key_size = map->key_size;



	hash = htab_map_hash(key, key_size);

	b = __select_bucket(htab, hash);

	head = &b->head;



	raw_spin_lock_irqsave(&htab->lock, flags);



	head = select_bucket(htab, hash);

	raw_spin_lock_irqsave(&b->lock, flags);



	l = lookup_elem_raw(head, hash, key, key_size);



	if (l) {

		hlist_del_rcu(&l->hash_node);

		htab->count--;

		atomic_dec(&htab->count);

		kfree_rcu(l, rcu);

		ret = 0;

	}



	raw_spin_unlock_irqrestore(&htab->lock, flags);

	raw_spin_unlock_irqrestore(&b->lock, flags);

	return ret;

}
@@ -339,7 +351,7 @@ static void delete_all_elements(struct bpf_htab *htab) 


		hlist_for_each_entry_safe(l, n, head, hash_node) {

			hlist_del_rcu(&l->hash_node);

			htab->count--;

			atomic_dec(&htab->count);

			kfree(l);

		}

	}

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