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mptcp: micro-optimize __mptcp_move_skb()
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After the RX path refactor the mentioned function is expected to run
frequently, let's optimize it a bit.

Scan for ready subflow from the last processed one, and stop after
traversing the list once or reaching the msk memory limit - instead of
looking for dubious per-subflow conditions.
Also re-order the memory limit checks, to avoid duplicate tests.

Signed-off-by: Paolo Abeni <[email protected]>
Reviewed-by: Mat Martineau <[email protected]>
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@matttbe
Paolo Abeni authored and matttbe committed Jan 3, 2025
1 parent c713e38 commit af0a2b6
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Showing 2 changed files with 52 additions and 61 deletions.
111 changes: 50 additions & 61 deletions net/mptcp/protocol.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -567,15 +567,13 @@ static void mptcp_dss_corruption(struct mptcp_sock *msk, struct sock *ssk)
}

static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
struct sock *ssk,
unsigned int *bytes)
struct sock *ssk)
{
struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
struct sock *sk = (struct sock *)msk;
unsigned int moved = 0;
bool more_data_avail;
struct tcp_sock *tp;
bool done = false;
bool ret = false;

pr_debug("msk=%p ssk=%p\n", msk, ssk);
tp = tcp_sk(ssk);
Expand All @@ -585,20 +583,16 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
struct sk_buff *skb;
bool fin;

if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
break;

/* try to move as much data as available */
map_remaining = subflow->map_data_len -
mptcp_subflow_get_map_offset(subflow);

skb = skb_peek(&ssk->sk_receive_queue);
if (!skb) {
/* With racing move_skbs_to_msk() and __mptcp_move_skbs(),
* a different CPU can have already processed the pending
* data, stop here or we can enter an infinite loop
*/
if (!moved)
done = true;
if (unlikely(!skb))
break;
}

if (__mptcp_check_fallback(msk)) {
/* Under fallback skbs have no MPTCP extension and TCP could
Expand All @@ -611,19 +605,13 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,

offset = seq - TCP_SKB_CB(skb)->seq;
fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
if (fin) {
done = true;
if (fin)
seq++;
}

if (offset < skb->len) {
size_t len = skb->len - offset;

if (tp->urg_data)
done = true;

if (__mptcp_move_skb(msk, ssk, skb, offset, len))
moved += len;
ret = __mptcp_move_skb(msk, ssk, skb, offset, len) || ret;
seq += len;

if (unlikely(map_remaining < len)) {
Expand All @@ -637,22 +625,16 @@ static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
}

sk_eat_skb(ssk, skb);
done = true;
}

WRITE_ONCE(tp->copied_seq, seq);
more_data_avail = mptcp_subflow_data_available(ssk);

if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf) {
done = true;
break;
}
} while (more_data_avail);

if (moved > 0)
if (ret)
msk->last_data_recv = tcp_jiffies32;
*bytes += moved;
return done;
return ret;
}

static bool __mptcp_ofo_queue(struct mptcp_sock *msk)
Expand Down Expand Up @@ -746,9 +728,9 @@ void __mptcp_error_report(struct sock *sk)
static bool move_skbs_to_msk(struct mptcp_sock *msk, struct sock *ssk)
{
struct sock *sk = (struct sock *)msk;
unsigned int moved = 0;
bool moved;

__mptcp_move_skbs_from_subflow(msk, ssk, &moved);
moved = __mptcp_move_skbs_from_subflow(msk, ssk);
__mptcp_ofo_queue(msk);
if (unlikely(ssk->sk_err)) {
if (!sock_owned_by_user(sk))
Expand All @@ -764,7 +746,7 @@ static bool move_skbs_to_msk(struct mptcp_sock *msk, struct sock *ssk)
*/
if (mptcp_pending_data_fin(sk, NULL))
mptcp_schedule_work(sk);
return moved > 0;
return moved;
}

static void __mptcp_rcvbuf_update(struct sock *sk, struct sock *ssk)
Expand All @@ -779,10 +761,6 @@ static void __mptcp_data_ready(struct sock *sk, struct sock *ssk)

__mptcp_rcvbuf_update(sk, ssk);

/* over limit? can't append more skbs to msk, Also, no need to wake-up*/
if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
return;

/* Wake-up the reader only for in-sequence data */
if (move_skbs_to_msk(msk, ssk) && mptcp_epollin_ready(sk))
sk->sk_data_ready(sk);
Expand Down Expand Up @@ -882,20 +860,6 @@ bool mptcp_schedule_work(struct sock *sk)
return false;
}

static struct sock *mptcp_subflow_recv_lookup(const struct mptcp_sock *msk)
{
struct mptcp_subflow_context *subflow;

msk_owned_by_me(msk);

mptcp_for_each_subflow(msk, subflow) {
if (READ_ONCE(subflow->data_avail))
return mptcp_subflow_tcp_sock(subflow);
}

return NULL;
}

static bool mptcp_skb_can_collapse_to(u64 write_seq,
const struct sk_buff *skb,
const struct mptcp_ext *mpext)
Expand Down Expand Up @@ -2033,37 +1997,62 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied)
msk->rcvq_space.time = mstamp;
}

static struct mptcp_subflow_context *
__mptcp_first_ready_from(struct mptcp_sock *msk,
struct mptcp_subflow_context *subflow)
{
struct mptcp_subflow_context *start_subflow = subflow;

while (!READ_ONCE(subflow->data_avail)) {
subflow = mptcp_next_subflow(msk, subflow);
if (subflow == start_subflow)
return NULL;
}
return subflow;
}

static bool __mptcp_move_skbs(struct sock *sk)
{
struct mptcp_subflow_context *subflow;
struct mptcp_sock *msk = mptcp_sk(sk);
unsigned int moved = 0;
bool ret, done;
bool ret = false;

if (list_empty(&msk->conn_list))
return false;

/* verify we can move any data from the subflow, eventually updating */
if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
mptcp_for_each_subflow(msk, subflow)
__mptcp_rcvbuf_update(sk, subflow->tcp_sock);

if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
return false;

do {
struct sock *ssk = mptcp_subflow_recv_lookup(msk);
subflow = list_first_entry(&msk->conn_list,
struct mptcp_subflow_context, node);
for (;;) {
struct sock *ssk;
bool slowpath;

if (unlikely(!ssk))
/*
* As an optimization avoid traversing the subflows list
* and ev. acquiring the subflow socket lock before baling out
*/
if (sk_rmem_alloc_get(sk) > sk->sk_rcvbuf)
break;

slowpath = lock_sock_fast(ssk);
done = __mptcp_move_skbs_from_subflow(msk, ssk, &moved);
subflow = __mptcp_first_ready_from(msk, subflow);
if (!subflow)
break;

ssk = mptcp_subflow_tcp_sock(subflow);
slowpath = lock_sock_fast(ssk);
ret = __mptcp_move_skbs_from_subflow(msk, ssk) || ret;
if (unlikely(ssk->sk_err))
__mptcp_error_report(sk);
unlock_sock_fast(ssk, slowpath);
} while (!done);

ret = moved > 0 || __mptcp_ofo_queue(msk);
subflow = mptcp_next_subflow(msk, subflow);
}

__mptcp_ofo_queue(msk);
if (ret)
mptcp_check_data_fin((struct sock *)msk);
return ret;
Expand Down
2 changes: 2 additions & 0 deletions net/mptcp/protocol.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -351,6 +351,8 @@ struct mptcp_sock {
list_for_each_entry(__subflow, &((__msk)->conn_list), node)
#define mptcp_for_each_subflow_safe(__msk, __subflow, __tmp) \
list_for_each_entry_safe(__subflow, __tmp, &((__msk)->conn_list), node)
#define mptcp_next_subflow(__msk, __subflow) \
list_next_entry_circular(__subflow, &((__msk)->conn_list), node)

extern struct genl_family mptcp_genl_family;

Expand Down

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