Hi,
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
kernel/bpf/hashtab.c | 64 +++++++++++++++++++++++++++++++---------------------
1 file changed, 38 insertions(+), 26 deletions(-)
Thanks,
Ming Lei
Preparing for removing global per-hashtable lock, so
the counter need to be defined as aotmic_t first.
Acked-by: Daniel Borkmann <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
---
kernel/bpf/hashtab.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 34777b3..2615388 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -18,7 +18,7 @@ struct bpf_htab {
struct bpf_map map;
struct hlist_head *buckets;
raw_spinlock_t lock;
- u32 count; /* number of elements in this hashtable */
+ 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 */
};
@@ -106,7 +106,7 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
INIT_HLIST_HEAD(&htab->buckets[i]);
raw_spin_lock_init(&htab->lock);
- htab->count = 0;
+ atomic_set(&htab->count, 0);
return &htab->map;
@@ -256,7 +256,7 @@ static int htab_map_update_elem(struct bpf_map *map, void *key, void *value,
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
*/
@@ -284,7 +284,7 @@ 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);
@@ -319,7 +319,7 @@ static int htab_map_delete_elem(struct bpf_map *map, void *key)
if (l) {
hlist_del_rcu(&l->hash_node);
- htab->count--;
+ atomic_dec(&htab->count);
kfree_rcu(l, rcu);
ret = 0;
}
@@ -339,7 +339,7 @@ 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);
}
}
--
1.9.1
The spinlock is just used for protecting the per-bucket
hlist, so it isn't needed for selecting bucket.
Acked-by: Daniel Borkmann <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
---
kernel/bpf/hashtab.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 2615388..d857fcb 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -248,12 +248,11 @@ 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);
/* bpf_map_update_elem() can be called in_irq() */
raw_spin_lock_irqsave(&htab->lock, flags);
- head = select_bucket(htab, l_new->hash);
-
l_old = lookup_elem_raw(head, l_new->hash, key, key_size);
if (!l_old && unlikely(atomic_read(&htab->count) >= map->max_entries)) {
@@ -310,11 +309,10 @@ 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);
raw_spin_lock_irqsave(&htab->lock, flags);
- head = select_bucket(htab, hash);
-
l = lookup_elem_raw(head, hash, key, key_size);
if (l) {
--
1.9.1
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: Ming Lei <[email protected]>
---
kernel/bpf/hashtab.c | 50 ++++++++++++++++++++++++++++++++------------------
1 file changed, 32 insertions(+), 18 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index d857fcb..c5b30fd 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -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;
}
--
1.9.1
On 12/29/2015 03:40 PM, Ming Lei wrote:
> 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: Ming Lei <[email protected]>
Looks better, thanks!
Acked-by: Daniel Borkmann <[email protected]>
From: Ming Lei <[email protected]>
Date: Tue, 29 Dec 2015 22:40:24 +0800
> Hi,
>
> 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
Series applied, thanks.