From: Alexei Starovoitov <ast@xxxxxxxxxx>
Doing call_rcu() million times a second becomes a bottle neck.
Convert non-preallocated hash map from call_rcu to SLAB_TYPESAFE_BY_RCU.
The rcu critical section is no longer observed for one htab element
which makes non-preallocated hash map behave just like preallocated hash map.
The map elements are released back to kernel memory after observing
rcu critical section.
This improves 'map_perf_test 4' performance from 100k events per second
to 250k events per second.
bpf_mem_alloc + percpu_counter + typesafe_by_rcu provide 10x performance
boost to non-preallocated hash map and make it within few % of preallocated map
while consuming fraction of memory.
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
---
kernel/bpf/hashtab.c | 8 ++++++--
kernel/bpf/memalloc.c | 2 +-
tools/testing/selftests/bpf/progs/timer.c | 11 -----------
3 files changed, 7 insertions(+), 14 deletions(-)
diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 8f68c6e13339..299ab98f9811 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -940,8 +940,12 @@ static void free_htab_elem(struct bpf_htab *htab, struct htab_elem *l)
__pcpu_freelist_push(&htab->freelist, &l->fnode);
} else {
dec_elem_count(htab);
- l->htab = htab;
- call_rcu(&l->rcu, htab_elem_free_rcu);
+ if (htab->map.map_type == BPF_MAP_TYPE_PERCPU_HASH) {
+ l->htab = htab;
+ call_rcu(&l->rcu, htab_elem_free_rcu);
+ } else {
+ htab_elem_free(htab, l);
+ }
}
}
diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c
index 293380eaea41..cfa07f539eda 100644
--- a/kernel/bpf/memalloc.c
+++ b/kernel/bpf/memalloc.c
@@ -276,7 +276,7 @@ int bpf_mem_alloc_init(struct bpf_mem_alloc *ma, int size)
return -ENOMEM;
size += LLIST_NODE_SZ; /* room for llist_node */
snprintf(buf, sizeof(buf), "bpf-%u", size);
- kmem_cache = kmem_cache_create(buf, size, 8, 0, NULL);
+ kmem_cache = kmem_cache_create(buf, size, 8, SLAB_TYPESAFE_BY_RCU, NULL);
if (!kmem_cache) {
free_percpu(pc);
return -ENOMEM;
diff --git a/tools/testing/selftests/bpf/progs/timer.c b/tools/testing/selftests/bpf/progs/timer.c
index 5f5309791649..0053c5402173 100644
--- a/tools/testing/selftests/bpf/progs/timer.c
+++ b/tools/testing/selftests/bpf/progs/timer.c
@@ -208,17 +208,6 @@ static int timer_cb2(void *map, int *key, struct hmap_elem *val)
*/
bpf_map_delete_elem(map, key);
- /* in non-preallocated hashmap both 'key' and 'val' are RCU
- * protected and still valid though this element was deleted
- * from the map. Arm this timer for ~35 seconds. When callback
- * finishes the call_rcu will invoke:
- * htab_elem_free_rcu
- * check_and_free_timer
- * bpf_timer_cancel_and_free
- * to cancel this 35 second sleep and delete the timer for real.
- */
- if (bpf_timer_start(&val->timer, 1ull << 35, 0) != 0)
- err |= 256;
ok |= 4;
}
return 0;
--
2.30.2
