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mptcp: refactor sndbuf auto-tuning.
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The MPTCP protocol account for the data enqueued on all the subflows
to the main socket send buffer, while the send buffer auto-tuning
algorithm set the main socket send buffer size as the max size among
the subflows.

That causes bad performances when at least one subflow is sndbuf
limited, e.g. due to very high latency, as the MPTCP scheduler can't
even fill such buffer.

Change the send-buffer auto-tuning algorithm to compute the main socket
send buffer size as the sum of all the subflows buffer size.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
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@intel-lab-lkp
Paolo Abeni authored and intel-lab-lkp committed Sep 15, 2023
1 parent bd72ba3 commit 09f40ee
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Showing 3 changed files with 67 additions and 9 deletions.
19 changes: 17 additions & 2 deletions net/mptcp/protocol.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -891,6 +891,7 @@ static bool __mptcp_finish_join(struct mptcp_sock *msk, struct sock *ssk)
mptcp_sockopt_sync_locked(msk, ssk);
mptcp_subflow_joined(msk, ssk);
mptcp_stop_tout_timer(sk);
__mptcp_propagate_sndbuf(sk, ssk);
return true;
}

Expand Down Expand Up @@ -1077,15 +1078,16 @@ static void mptcp_enter_memory_pressure(struct sock *sk)
struct mptcp_sock *msk = mptcp_sk(sk);
bool first = true;

sk_stream_moderate_sndbuf(sk);
mptcp_for_each_subflow(msk, subflow) {
struct sock *ssk = mptcp_subflow_tcp_sock(subflow);

if (first)
tcp_enter_memory_pressure(ssk);
sk_stream_moderate_sndbuf(ssk);

first = false;
}
__mptcp_sync_sndbuf(sk);
}

/* ensure we get enough memory for the frag hdr, beyond some minimal amount of
Expand Down Expand Up @@ -2436,6 +2438,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
WRITE_ONCE(msk->first, NULL);

out:
__mptcp_sync_sndbuf(sk);
if (need_push)
__mptcp_push_pending(sk, 0);

Expand Down Expand Up @@ -3214,7 +3217,7 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk,
* uses the correct data
*/
mptcp_copy_inaddrs(nsk, ssk);
mptcp_propagate_sndbuf(nsk, ssk);
__mptcp_propagate_sndbuf(nsk, ssk);

mptcp_rcv_space_init(msk, ssk);
bh_unlock_sock(nsk);
Expand Down Expand Up @@ -3392,6 +3395,8 @@ static void mptcp_release_cb(struct sock *sk)
__mptcp_set_connected(sk);
if (__test_and_clear_bit(MPTCP_ERROR_REPORT, &msk->cb_flags))
__mptcp_error_report(sk);
if (__test_and_clear_bit(MPTCP_SYNC_SNDBUF, &msk->cb_flags))
__mptcp_sync_sndbuf(sk);
}

__mptcp_update_rmem(sk);
Expand Down Expand Up @@ -3437,6 +3442,15 @@ void mptcp_subflow_process_delegated(struct sock *ssk)
mptcp_data_unlock(sk);
mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_SEND);
}
if (test_bit(MPTCP_DELEGATE_SNDBUF, &subflow->delegated_status)) {
mptcp_data_lock(sk);
if (!sock_owned_by_user(sk))
__mptcp_sync_sndbuf(sk);
else
__set_bit(MPTCP_SYNC_SNDBUF, &mptcp_sk(sk)->cb_flags);
mptcp_data_unlock(sk);
mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_SNDBUF);
}
if (test_bit(MPTCP_DELEGATE_ACK, &subflow->delegated_status)) {
schedule_3rdack_retransmission(ssk);
mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_ACK);
Expand Down Expand Up @@ -3523,6 +3537,7 @@ bool mptcp_finish_join(struct sock *ssk)
/* active subflow, already present inside the conn_list */
if (!list_empty(&subflow->node)) {
mptcp_subflow_joined(msk, ssk);
mptcp_propagate_sndbuf(parent, ssk);
return true;
}

Expand Down
54 changes: 49 additions & 5 deletions net/mptcp/protocol.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -123,6 +123,7 @@
#define MPTCP_RETRANSMIT 4
#define MPTCP_FLUSH_JOIN_LIST 5
#define MPTCP_CONNECTED 6
#define MPTCP_SYNC_SNDBUF 7

struct mptcp_skb_cb {
u64 map_seq;
Expand Down Expand Up @@ -446,6 +447,7 @@ DECLARE_PER_CPU(struct mptcp_delegated_action, mptcp_delegated_actions);

#define MPTCP_DELEGATE_SEND 0
#define MPTCP_DELEGATE_ACK 1
#define MPTCP_DELEGATE_SNDBUF 2

/* MPTCP subflow context */
struct mptcp_subflow_context {
Expand Down Expand Up @@ -518,6 +520,9 @@ struct mptcp_subflow_context {

u32 setsockopt_seq;
u32 stale_rcv_tstamp;
int cached_sndbuf; /* sndbuf size when last synced with the msk sndbuf,
* protected by the msk socket lock
*/

struct sock *tcp_sock; /* tcp sk backpointer */
struct sock *conn; /* parent mptcp_sock */
Expand Down Expand Up @@ -781,13 +786,52 @@ static inline bool mptcp_data_fin_enabled(const struct mptcp_sock *msk)
READ_ONCE(msk->write_seq) == READ_ONCE(msk->snd_nxt);
}

static inline bool mptcp_propagate_sndbuf(struct sock *sk, struct sock *ssk)
static inline void __mptcp_sync_sndbuf(struct sock *sk)
{
if ((sk->sk_userlocks & SOCK_SNDBUF_LOCK) || ssk->sk_sndbuf <= READ_ONCE(sk->sk_sndbuf))
return false;
struct mptcp_subflow_context *subflow;
int ssk_sndbuf, new_sndbuf;

if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
return;

new_sndbuf = sock_net(sk)->ipv4.sysctl_tcp_wmem[0];
mptcp_for_each_subflow(mptcp_sk(sk), subflow) {
ssk_sndbuf = READ_ONCE(mptcp_subflow_tcp_sock(subflow)->sk_sndbuf);

subflow->cached_sndbuf = ssk_sndbuf;
new_sndbuf += ssk_sndbuf;
}

/* the msk max wmem limit is <nr_subflows> * tcp wmem[2] */
WRITE_ONCE(sk->sk_sndbuf, new_sndbuf);
}

/* The called held both the msk socket and the subflow socket locks,
* possibly under BH
*/
static inline void __mptcp_propagate_sndbuf(struct sock *sk, struct sock *ssk)
{
struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);

if (READ_ONCE(ssk->sk_sndbuf) - subflow->cached_sndbuf)
__mptcp_sync_sndbuf(sk);
}

/* the caller held only the subflow socket lock, either in process or
* BH context. Additionally this can be called under the msk data lock,
* so we can't acquire such lock here: let the delegate action acquires
* the needed locks in suitable order.
*/
static inline void mptcp_propagate_sndbuf(struct sock *sk, struct sock *ssk)
{
struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);

if (likely(READ_ONCE(ssk->sk_sndbuf) == subflow->cached_sndbuf))
return;

WRITE_ONCE(sk->sk_sndbuf, ssk->sk_sndbuf);
return true;
local_bh_disable();
mptcp_subflow_delegate(subflow, MPTCP_DELEGATE_SNDBUF);
local_bh_enable();
}

static inline void mptcp_write_space(struct sock *sk)
Expand Down
3 changes: 1 addition & 2 deletions net/mptcp/subflow.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -421,6 +421,7 @@ static bool subflow_use_different_dport(struct mptcp_sock *msk, const struct soc

void __mptcp_set_connected(struct sock *sk)
{
__mptcp_propagate_sndbuf(sk, mptcp_sk(sk)->first);
if (sk->sk_state == TCP_SYN_SENT) {
inet_sk_state_store(sk, TCP_ESTABLISHED);
sk->sk_state_change(sk);
Expand Down Expand Up @@ -472,7 +473,6 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
return;

msk = mptcp_sk(parent);
mptcp_propagate_sndbuf(parent, sk);
subflow->rel_write_seq = 1;
subflow->conn_finished = 1;
subflow->ssn_offset = TCP_SKB_CB(skb)->seq;
Expand Down Expand Up @@ -1728,7 +1728,6 @@ static void subflow_state_change(struct sock *sk)

msk = mptcp_sk(parent);
if (subflow_simultaneous_connect(sk)) {
mptcp_propagate_sndbuf(parent, sk);
mptcp_do_fallback(sk);
mptcp_rcv_space_init(msk, sk);
pr_fallback(msk);
Expand Down

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