[PATCH 5.11 772/775] wireguard: queueing: get rid of per-peer ring buffers

From: Jason A. Donenfeld Jason@zx2c4.com

commit 8b5553ace83cced775eefd0f3f18b5c6214ccf7a upstream.

Having two ring buffers per-peer means that every peer results in two massive ring allocations. On an 8-core x86_64 machine, this commit reduces the per-peer allocation from 18,688 bytes to 1,856 bytes, which is an 90% reduction. Ninety percent! With some single-machine deployments approaching 500,000 peers, we're talking about a reduction from 7 gigs of memory down to 700 megs of memory.

In order to get rid of these per-peer allocations, this commit switches to using a list-based queueing approach. Currently GSO fragments are chained together using the skb->next pointer (the skb_list_* singly linked list approach), so we form the per-peer queue around the unused skb->prev pointer (which sort of makes sense because the links are pointing backwards). Use of skb_queue_* is not possible here, because that is based on doubly linked lists and spinlocks. Multiple cores can write into the queue at any given time, because its writes occur in the start_xmit path or in the udp_recv path. But reads happen in a single workqueue item per-peer, amounting to a multi-producer, single-consumer paradigm.

The MPSC queue is implemented locklessly and never blocks. However, it is not linearizable (though it is serializable), with a very tight and unlikely race on writes, which, when hit (some tiny fraction of the 0.15% of partial adds on a fully loaded 16-core x86_64 system), causes the queue reader to terminate early. However, because every packet sent queues up the same workqueue item after it is fully added, the worker resumes again, and stopping early isn't actually a problem, since at that point the packet wouldn't have yet been added to the encryption queue. These properties allow us to avoid disabling interrupts or spinning. The design is based on Dmitry Vyukov's algorithm [1].

Performance-wise, ordinarily list-based queues aren't preferable to ringbuffers, because of cache misses when following pointers around. However, we *already* have to follow the adjacent pointers when working through fragments, so there shouldn't actually be any change there. A potential downside is that dequeueing is a bit more complicated, but the ptr_ring structure used prior had a spinlock when dequeueing, so all and all the difference appears to be a wash.

Actually, from profiling, the biggest performance hit, by far, of this commit winds up being atomic_add_unless(count, 1, max) and atomic_ dec(count), which account for the majority of CPU time, according to perf. In that sense, the previous ring buffer was superior in that it could check if it was full by head==tail, which the list-based approach cannot do.

But all and all, this enables us to get massive memory savings, allowing WireGuard to scale for real world deployments, without taking much of a performance hit.

[1] http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-mpsc-nod...

Reviewed-by: Dmitry Vyukov dvyukov@google.com Reviewed-by: Toke Høiland-Jørgensen toke@redhat.com Fixes: e7096c131e51 ("net: WireGuard secure network tunnel") Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/wireguard/device.c | 12 ++--- drivers/net/wireguard/device.h | 15 +++--- drivers/net/wireguard/peer.c | 28 ++++-------- drivers/net/wireguard/peer.h | 4 - drivers/net/wireguard/queueing.c | 86 +++++++++++++++++++++++++++++++-------- drivers/net/wireguard/queueing.h | 45 ++++++++++++++------ drivers/net/wireguard/receive.c | 16 ++----- drivers/net/wireguard/send.c | 31 ++++---------- 8 files changed, 144 insertions(+), 93 deletions(-)

--- a/drivers/net/wireguard/device.c +++ b/drivers/net/wireguard/device.c @@ -235,8 +235,8 @@ static void wg_destruct(struct net_devic destroy_workqueue(wg->handshake_receive_wq); destroy_workqueue(wg->handshake_send_wq); destroy_workqueue(wg->packet_crypt_wq); - wg_packet_queue_free(&wg->decrypt_queue, true); - wg_packet_queue_free(&wg->encrypt_queue, true); + wg_packet_queue_free(&wg->decrypt_queue); + wg_packet_queue_free(&wg->encrypt_queue); rcu_barrier(); /* Wait for all the peers to be actually freed. */ wg_ratelimiter_uninit(); memzero_explicit(&wg->static_identity, sizeof(wg->static_identity)); @@ -338,12 +338,12 @@ static int wg_newlink(struct net *src_ne goto err_destroy_handshake_send;

ret = wg_packet_queue_init(&wg->encrypt_queue, wg_packet_encrypt_worker, - true, MAX_QUEUED_PACKETS); + MAX_QUEUED_PACKETS); if (ret < 0) goto err_destroy_packet_crypt;

ret = wg_packet_queue_init(&wg->decrypt_queue, wg_packet_decrypt_worker, - true, MAX_QUEUED_PACKETS); + MAX_QUEUED_PACKETS); if (ret < 0) goto err_free_encrypt_queue;

@@ -368,9 +368,9 @@ static int wg_newlink(struct net *src_ne err_uninit_ratelimiter: wg_ratelimiter_uninit(); err_free_decrypt_queue: - wg_packet_queue_free(&wg->decrypt_queue, true); + wg_packet_queue_free(&wg->decrypt_queue); err_free_encrypt_queue: - wg_packet_queue_free(&wg->encrypt_queue, true); + wg_packet_queue_free(&wg->encrypt_queue); err_destroy_packet_crypt: destroy_workqueue(wg->packet_crypt_wq); err_destroy_handshake_send: --- a/drivers/net/wireguard/device.h +++ b/drivers/net/wireguard/device.h @@ -27,13 +27,14 @@ struct multicore_worker {

struct crypt_queue { struct ptr_ring ring; - union { - struct { - struct multicore_worker __percpu *worker; - int last_cpu; - }; - struct work_struct work; - }; + struct multicore_worker __percpu *worker; + int last_cpu; +}; + +struct prev_queue { + struct sk_buff *head, *tail, *peeked; + struct { struct sk_buff *next, *prev; } empty; // Match first 2 members of struct sk_buff. + atomic_t count; };

struct wg_device { --- a/drivers/net/wireguard/peer.c +++ b/drivers/net/wireguard/peer.c @@ -32,27 +32,22 @@ struct wg_peer *wg_peer_create(struct wg peer = kzalloc(sizeof(*peer), GFP_KERNEL); if (unlikely(!peer)) return ERR_PTR(ret); - peer->device = wg; + if (dst_cache_init(&peer->endpoint_cache, GFP_KERNEL)) + goto err;

+ peer->device = wg; wg_noise_handshake_init(&peer->handshake, &wg->static_identity, public_key, preshared_key, peer); - if (dst_cache_init(&peer->endpoint_cache, GFP_KERNEL)) - goto err_1; - if (wg_packet_queue_init(&peer->tx_queue, wg_packet_tx_worker, false, - MAX_QUEUED_PACKETS)) - goto err_2; - if (wg_packet_queue_init(&peer->rx_queue, NULL, false, - MAX_QUEUED_PACKETS)) - goto err_3; - peer->internal_id = atomic64_inc_return(&peer_counter); peer->serial_work_cpu = nr_cpumask_bits; wg_cookie_init(&peer->latest_cookie); wg_timers_init(peer); wg_cookie_checker_precompute_peer_keys(peer); spin_lock_init(&peer->keypairs.keypair_update_lock); - INIT_WORK(&peer->transmit_handshake_work, - wg_packet_handshake_send_worker); + INIT_WORK(&peer->transmit_handshake_work, wg_packet_handshake_send_worker); + INIT_WORK(&peer->transmit_packet_work, wg_packet_tx_worker); + wg_prev_queue_init(&peer->tx_queue); + wg_prev_queue_init(&peer->rx_queue); rwlock_init(&peer->endpoint_lock); kref_init(&peer->refcount); skb_queue_head_init(&peer->staged_packet_queue); @@ -68,11 +63,7 @@ struct wg_peer *wg_peer_create(struct wg pr_debug("%s: Peer %llu created\n", wg->dev->name, peer->internal_id); return peer;

-err_3: - wg_packet_queue_free(&peer->tx_queue, false); -err_2: - dst_cache_destroy(&peer->endpoint_cache); -err_1: +err: kfree(peer); return ERR_PTR(ret); } @@ -197,8 +188,7 @@ static void rcu_release(struct rcu_head struct wg_peer *peer = container_of(rcu, struct wg_peer, rcu);

dst_cache_destroy(&peer->endpoint_cache); - wg_packet_queue_free(&peer->rx_queue, false); - wg_packet_queue_free(&peer->tx_queue, false); + WARN_ON(wg_prev_queue_peek(&peer->tx_queue) || wg_prev_queue_peek(&peer->rx_queue));

/* The final zeroing takes care of clearing any remaining handshake key * material and other potentially sensitive information. --- a/drivers/net/wireguard/peer.h +++ b/drivers/net/wireguard/peer.h @@ -36,7 +36,7 @@ struct endpoint {

struct wg_peer { struct wg_device *device; - struct crypt_queue tx_queue, rx_queue; + struct prev_queue tx_queue, rx_queue; struct sk_buff_head staged_packet_queue; int serial_work_cpu; struct noise_keypairs keypairs; @@ -45,7 +45,7 @@ struct wg_peer { rwlock_t endpoint_lock; struct noise_handshake handshake; atomic64_t last_sent_handshake; - struct work_struct transmit_handshake_work, clear_peer_work; + struct work_struct transmit_handshake_work, clear_peer_work, transmit_packet_work; struct cookie latest_cookie; struct hlist_node pubkey_hash; u64 rx_bytes, tx_bytes; --- a/drivers/net/wireguard/queueing.c +++ b/drivers/net/wireguard/queueing.c @@ -9,8 +9,7 @@ struct multicore_worker __percpu * wg_packet_percpu_multicore_worker_alloc(work_func_t function, void *ptr) { int cpu; - struct multicore_worker __percpu *worker = - alloc_percpu(struct multicore_worker); + struct multicore_worker __percpu *worker = alloc_percpu(struct multicore_worker);

if (!worker) return NULL; @@ -23,7 +22,7 @@ wg_packet_percpu_multicore_worker_alloc( }

int wg_packet_queue_init(struct crypt_queue *queue, work_func_t function, - bool multicore, unsigned int len) + unsigned int len) { int ret;

@@ -31,25 +30,78 @@ int wg_packet_queue_init(struct crypt_qu ret = ptr_ring_init(&queue->ring, len, GFP_KERNEL); if (ret) return ret; - if (function) { - if (multicore) { - queue->worker = wg_packet_percpu_multicore_worker_alloc( - function, queue); - if (!queue->worker) { - ptr_ring_cleanup(&queue->ring, NULL); - return -ENOMEM; - } - } else { - INIT_WORK(&queue->work, function); - } + queue->worker = wg_packet_percpu_multicore_worker_alloc(function, queue); + if (!queue->worker) { + ptr_ring_cleanup(&queue->ring, NULL); + return -ENOMEM; } return 0; }

-void wg_packet_queue_free(struct crypt_queue *queue, bool multicore) +void wg_packet_queue_free(struct crypt_queue *queue) { - if (multicore) - free_percpu(queue->worker); + free_percpu(queue->worker); WARN_ON(!__ptr_ring_empty(&queue->ring)); ptr_ring_cleanup(&queue->ring, NULL); } + +#define NEXT(skb) ((skb)->prev) +#define STUB(queue) ((struct sk_buff *)&queue->empty) + +void wg_prev_queue_init(struct prev_queue *queue) +{ + NEXT(STUB(queue)) = NULL; + queue->head = queue->tail = STUB(queue); + queue->peeked = NULL; + atomic_set(&queue->count, 0); + BUILD_BUG_ON( + offsetof(struct sk_buff, next) != offsetof(struct prev_queue, empty.next) - + offsetof(struct prev_queue, empty) || + offsetof(struct sk_buff, prev) != offsetof(struct prev_queue, empty.prev) - + offsetof(struct prev_queue, empty)); +} + +static void __wg_prev_queue_enqueue(struct prev_queue *queue, struct sk_buff *skb) +{ + WRITE_ONCE(NEXT(skb), NULL); + WRITE_ONCE(NEXT(xchg_release(&queue->head, skb)), skb); +} + +bool wg_prev_queue_enqueue(struct prev_queue *queue, struct sk_buff *skb) +{ + if (!atomic_add_unless(&queue->count, 1, MAX_QUEUED_PACKETS)) + return false; + __wg_prev_queue_enqueue(queue, skb); + return true; +} + +struct sk_buff *wg_prev_queue_dequeue(struct prev_queue *queue) +{ + struct sk_buff *tail = queue->tail, *next = smp_load_acquire(&NEXT(tail)); + + if (tail == STUB(queue)) { + if (!next) + return NULL; + queue->tail = next; + tail = next; + next = smp_load_acquire(&NEXT(next)); + } + if (next) { + queue->tail = next; + atomic_dec(&queue->count); + return tail; + } + if (tail != READ_ONCE(queue->head)) + return NULL; + __wg_prev_queue_enqueue(queue, STUB(queue)); + next = smp_load_acquire(&NEXT(tail)); + if (next) { + queue->tail = next; + atomic_dec(&queue->count); + return tail; + } + return NULL; +} + +#undef NEXT +#undef STUB --- a/drivers/net/wireguard/queueing.h +++ b/drivers/net/wireguard/queueing.h @@ -17,12 +17,13 @@ struct wg_device; struct wg_peer; struct multicore_worker; struct crypt_queue; +struct prev_queue; struct sk_buff;

/* queueing.c APIs: */ int wg_packet_queue_init(struct crypt_queue *queue, work_func_t function, - bool multicore, unsigned int len); -void wg_packet_queue_free(struct crypt_queue *queue, bool multicore); + unsigned int len); +void wg_packet_queue_free(struct crypt_queue *queue); struct multicore_worker __percpu * wg_packet_percpu_multicore_worker_alloc(work_func_t function, void *ptr);

@@ -135,8 +136,31 @@ static inline int wg_cpumask_next_online return cpu; }

+void wg_prev_queue_init(struct prev_queue *queue); + +/* Multi producer */ +bool wg_prev_queue_enqueue(struct prev_queue *queue, struct sk_buff *skb); + +/* Single consumer */ +struct sk_buff *wg_prev_queue_dequeue(struct prev_queue *queue); + +/* Single consumer */ +static inline struct sk_buff *wg_prev_queue_peek(struct prev_queue *queue) +{ + if (queue->peeked) + return queue->peeked; + queue->peeked = wg_prev_queue_dequeue(queue); + return queue->peeked; +} + +/* Single consumer */ +static inline void wg_prev_queue_drop_peeked(struct prev_queue *queue) +{ + queue->peeked = NULL; +} + static inline int wg_queue_enqueue_per_device_and_peer( - struct crypt_queue *device_queue, struct crypt_queue *peer_queue, + struct crypt_queue *device_queue, struct prev_queue *peer_queue, struct sk_buff *skb, struct workqueue_struct *wq, int *next_cpu) { int cpu; @@ -145,8 +169,9 @@ static inline int wg_queue_enqueue_per_d /* We first queue this up for the peer ingestion, but the consumer * will wait for the state to change to CRYPTED or DEAD before. */ - if (unlikely(ptr_ring_produce_bh(&peer_queue->ring, skb))) + if (unlikely(!wg_prev_queue_enqueue(peer_queue, skb))) return -ENOSPC; + /* Then we queue it up in the device queue, which consumes the * packet as soon as it can. */ @@ -157,9 +182,7 @@ static inline int wg_queue_enqueue_per_d return 0; }

-static inline void wg_queue_enqueue_per_peer(struct crypt_queue *queue, - struct sk_buff *skb, - enum packet_state state) +static inline void wg_queue_enqueue_per_peer_tx(struct sk_buff *skb, enum packet_state state) { /* We take a reference, because as soon as we call atomic_set, the * peer can be freed from below us. @@ -167,14 +190,12 @@ static inline void wg_queue_enqueue_per_ struct wg_peer *peer = wg_peer_get(PACKET_PEER(skb));

atomic_set_release(&PACKET_CB(skb)->state, state); - queue_work_on(wg_cpumask_choose_online(&peer->serial_work_cpu, - peer->internal_id), - peer->device->packet_crypt_wq, &queue->work); + queue_work_on(wg_cpumask_choose_online(&peer->serial_work_cpu, peer->internal_id), + peer->device->packet_crypt_wq, &peer->transmit_packet_work); wg_peer_put(peer); }

-static inline void wg_queue_enqueue_per_peer_napi(struct sk_buff *skb, - enum packet_state state) +static inline void wg_queue_enqueue_per_peer_rx(struct sk_buff *skb, enum packet_state state) { /* We take a reference, because as soon as we call atomic_set, the * peer can be freed from below us. --- a/drivers/net/wireguard/receive.c +++ b/drivers/net/wireguard/receive.c @@ -444,7 +444,6 @@ packet_processed: int wg_packet_rx_poll(struct napi_struct *napi, int budget) { struct wg_peer *peer = container_of(napi, struct wg_peer, napi); - struct crypt_queue *queue = &peer->rx_queue; struct noise_keypair *keypair; struct endpoint endpoint; enum packet_state state; @@ -455,11 +454,10 @@ int wg_packet_rx_poll(struct napi_struct if (unlikely(budget <= 0)) return 0;

- while ((skb = __ptr_ring_peek(&queue->ring)) != NULL && + while ((skb = wg_prev_queue_peek(&peer->rx_queue)) != NULL && (state = atomic_read_acquire(&PACKET_CB(skb)->state)) != PACKET_STATE_UNCRYPTED) { - __ptr_ring_discard_one(&queue->ring); - peer = PACKET_PEER(skb); + wg_prev_queue_drop_peeked(&peer->rx_queue); keypair = PACKET_CB(skb)->keypair; free = true;

@@ -508,7 +506,7 @@ void wg_packet_decrypt_worker(struct wor enum packet_state state = likely(decrypt_packet(skb, PACKET_CB(skb)->keypair)) ? PACKET_STATE_CRYPTED : PACKET_STATE_DEAD; - wg_queue_enqueue_per_peer_napi(skb, state); + wg_queue_enqueue_per_peer_rx(skb, state); if (need_resched()) cond_resched(); } @@ -531,12 +529,10 @@ static void wg_packet_consume_data(struc if (unlikely(READ_ONCE(peer->is_dead))) goto err;

- ret = wg_queue_enqueue_per_device_and_peer(&wg->decrypt_queue, - &peer->rx_queue, skb, - wg->packet_crypt_wq, - &wg->decrypt_queue.last_cpu); + ret = wg_queue_enqueue_per_device_and_peer(&wg->decrypt_queue, &peer->rx_queue, skb, + wg->packet_crypt_wq, &wg->decrypt_queue.last_cpu); if (unlikely(ret == -EPIPE)) - wg_queue_enqueue_per_peer_napi(skb, PACKET_STATE_DEAD); + wg_queue_enqueue_per_peer_rx(skb, PACKET_STATE_DEAD); if (likely(!ret || ret == -EPIPE)) { rcu_read_unlock_bh(); return; --- a/drivers/net/wireguard/send.c +++ b/drivers/net/wireguard/send.c @@ -239,8 +239,7 @@ void wg_packet_send_keepalive(struct wg_ wg_packet_send_staged_packets(peer); }

-static void wg_packet_create_data_done(struct sk_buff *first, - struct wg_peer *peer) +static void wg_packet_create_data_done(struct wg_peer *peer, struct sk_buff *first) { struct sk_buff *skb, *next; bool is_keepalive, data_sent = false; @@ -262,22 +261,19 @@ static void wg_packet_create_data_done(s

void wg_packet_tx_worker(struct work_struct *work) { - struct crypt_queue *queue = container_of(work, struct crypt_queue, - work); + struct wg_peer *peer = container_of(work, struct wg_peer, transmit_packet_work); struct noise_keypair *keypair; enum packet_state state; struct sk_buff *first; - struct wg_peer *peer;

- while ((first = __ptr_ring_peek(&queue->ring)) != NULL && + while ((first = wg_prev_queue_peek(&peer->tx_queue)) != NULL && (state = atomic_read_acquire(&PACKET_CB(first)->state)) != PACKET_STATE_UNCRYPTED) { - __ptr_ring_discard_one(&queue->ring); - peer = PACKET_PEER(first); + wg_prev_queue_drop_peeked(&peer->tx_queue); keypair = PACKET_CB(first)->keypair;

if (likely(state == PACKET_STATE_CRYPTED)) - wg_packet_create_data_done(first, peer); + wg_packet_create_data_done(peer, first); else kfree_skb_list(first);

@@ -306,16 +302,14 @@ void wg_packet_encrypt_worker(struct wor break; } } - wg_queue_enqueue_per_peer(&PACKET_PEER(first)->tx_queue, first, - state); + wg_queue_enqueue_per_peer_tx(first, state); if (need_resched()) cond_resched(); } }

-static void wg_packet_create_data(struct sk_buff *first) +static void wg_packet_create_data(struct wg_peer *peer, struct sk_buff *first) { - struct wg_peer *peer = PACKET_PEER(first); struct wg_device *wg = peer->device; int ret = -EINVAL;

@@ -323,13 +317,10 @@ static void wg_packet_create_data(struct if (unlikely(READ_ONCE(peer->is_dead))) goto err;

- ret = wg_queue_enqueue_per_device_and_peer(&wg->encrypt_queue, - &peer->tx_queue, first, - wg->packet_crypt_wq, - &wg->encrypt_queue.last_cpu); + ret = wg_queue_enqueue_per_device_and_peer(&wg->encrypt_queue, &peer->tx_queue, first, + wg->packet_crypt_wq, &wg->encrypt_queue.last_cpu); if (unlikely(ret == -EPIPE)) - wg_queue_enqueue_per_peer(&peer->tx_queue, first, - PACKET_STATE_DEAD); + wg_queue_enqueue_per_peer_tx(first, PACKET_STATE_DEAD); err: rcu_read_unlock_bh(); if (likely(!ret || ret == -EPIPE)) @@ -393,7 +384,7 @@ void wg_packet_send_staged_packets(struc packets.prev->next = NULL; wg_peer_get(keypair->entry.peer); PACKET_CB(packets.next)->keypair = keypair; - wg_packet_create_data(packets.next); + wg_packet_create_data(peer, packets.next); return;

out_invalid: