diff options
| author | David Howells <dhowells@redhat.com> | 2022-11-11 13:47:35 +0000 |
|---|---|---|
| committer | David Howells <dhowells@redhat.com> | 2022-12-01 13:36:43 +0000 |
| commit | 5086d9a9dfec4866806da303115489b0606decb7 (patch) | |
| tree | 286a9b9c8cf80a3e853baa20cdf4bac9cc425718 /net/rxrpc/input.c | |
| parent | 32cf8edb079a6a687a2b5dba39a813a0bbd0ddf9 (diff) | |
rxrpc: Move the cwnd degradation after transmitting packets
When we've gone for >1RTT without transmitting a packet, we should reduce
the ssthresh and cut the cwnd by half (as suggested in RFC2861 sec 3.1).
However, we may receive ACK packets in a batch and the first of these may
cut the cwnd, preventing further transmission, and each subsequent one cuts
the cwnd yet further, reducing it to the floor and killing performance.
Fix this by moving the cwnd reset to after doing the transmission and
resetting the base time such that we don't cut the cwnd by half again for
at least another RTT.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Diffstat (limited to 'net/rxrpc/input.c')
| -rw-r--r-- | net/rxrpc/input.c | 49 |
1 files changed, 27 insertions, 22 deletions
diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c index 2988e3d0c1f6..d0e20e946e48 100644 --- a/net/rxrpc/input.c +++ b/net/rxrpc/input.c @@ -27,7 +27,6 @@ static void rxrpc_congestion_management(struct rxrpc_call *call, enum rxrpc_congest_change change = rxrpc_cong_no_change; unsigned int cumulative_acks = call->cong_cumul_acks; unsigned int cwnd = call->cong_cwnd; - ktime_t now; bool resend = false; summary->flight_size = @@ -57,27 +56,6 @@ static void rxrpc_congestion_management(struct rxrpc_call *call, summary->cumulative_acks = cumulative_acks; summary->dup_acks = call->cong_dup_acks; - /* If we haven't transmitted anything for >1RTT, we should reset the - * congestion management state. - */ - now = ktime_get_real(); - if ((call->cong_mode == RXRPC_CALL_SLOW_START || - call->cong_mode == RXRPC_CALL_CONGEST_AVOIDANCE) && - ktime_before(ktime_add_us(call->tx_last_sent, - call->peer->srtt_us >> 3), now) - ) { - trace_rxrpc_reset_cwnd(call, now); - change = rxrpc_cong_idle_reset; - rxrpc_inc_stat(call->rxnet, stat_tx_data_cwnd_reset); - summary->mode = RXRPC_CALL_SLOW_START; - if (RXRPC_TX_SMSS > 2190) - summary->cwnd = 2; - else if (RXRPC_TX_SMSS > 1095) - summary->cwnd = 3; - else - summary->cwnd = 4; - } - switch (call->cong_mode) { case RXRPC_CALL_SLOW_START: if (summary->saw_nacks) @@ -198,6 +176,33 @@ send_extra_data: } /* + * Degrade the congestion window if we haven't transmitted a packet for >1RTT. + */ +void rxrpc_congestion_degrade(struct rxrpc_call *call) +{ + ktime_t rtt, now; + + if (call->cong_mode != RXRPC_CALL_SLOW_START && + call->cong_mode != RXRPC_CALL_CONGEST_AVOIDANCE) + return; + if (call->state == RXRPC_CALL_CLIENT_AWAIT_REPLY) + return; + + rtt = ns_to_ktime(call->peer->srtt_us * (1000 / 8)); + now = ktime_get_real(); + if (!ktime_before(ktime_add(call->tx_last_sent, rtt), now)) + return; + + trace_rxrpc_reset_cwnd(call, now); + rxrpc_inc_stat(call->rxnet, stat_tx_data_cwnd_reset); + call->tx_last_sent = now; + call->cong_mode = RXRPC_CALL_SLOW_START; + call->cong_ssthresh = max_t(unsigned int, call->cong_ssthresh, + call->cong_cwnd * 3 / 4); + call->cong_cwnd = max_t(unsigned int, call->cong_cwnd / 2, RXRPC_MIN_CWND); +} + +/* * Apply a hard ACK by advancing the Tx window. */ static bool rxrpc_rotate_tx_window(struct rxrpc_call *call, rxrpc_seq_t to, |