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81365af13a
rxrpc_min_rtt_wlen is never used after it was introduced. So better to remove it. Reported-by: Hulk Robot <hulkci@huawei.com> Signed-off-by: Wang Hai <wanghai38@huawei.com> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
196 lines
5.8 KiB
C
196 lines
5.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/* RTT/RTO calculation.
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*
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* Adapted from TCP for AF_RXRPC by David Howells (dhowells@redhat.com)
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*
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* https://tools.ietf.org/html/rfc6298
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* https://tools.ietf.org/html/rfc1122#section-4.2.3.1
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* http://ccr.sigcomm.org/archive/1995/jan95/ccr-9501-partridge87.pdf
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*/
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#include <linux/net.h>
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#include "ar-internal.h"
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#define RXRPC_RTO_MAX ((unsigned)(120 * HZ))
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#define RXRPC_TIMEOUT_INIT ((unsigned)(1*HZ)) /* RFC6298 2.1 initial RTO value */
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#define rxrpc_jiffies32 ((u32)jiffies) /* As rxrpc_jiffies32 */
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static u32 rxrpc_rto_min_us(struct rxrpc_peer *peer)
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{
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return 200;
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}
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static u32 __rxrpc_set_rto(const struct rxrpc_peer *peer)
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{
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return _usecs_to_jiffies((peer->srtt_us >> 3) + peer->rttvar_us);
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}
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static u32 rxrpc_bound_rto(u32 rto)
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{
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return min(rto, RXRPC_RTO_MAX);
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}
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/*
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* Called to compute a smoothed rtt estimate. The data fed to this
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* routine either comes from timestamps, or from segments that were
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* known _not_ to have been retransmitted [see Karn/Partridge
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* Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
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* piece by Van Jacobson.
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* NOTE: the next three routines used to be one big routine.
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* To save cycles in the RFC 1323 implementation it was better to break
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* it up into three procedures. -- erics
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*/
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static void rxrpc_rtt_estimator(struct rxrpc_peer *peer, long sample_rtt_us)
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{
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long m = sample_rtt_us; /* RTT */
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u32 srtt = peer->srtt_us;
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/* The following amusing code comes from Jacobson's
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* article in SIGCOMM '88. Note that rtt and mdev
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* are scaled versions of rtt and mean deviation.
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* This is designed to be as fast as possible
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* m stands for "measurement".
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*
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* On a 1990 paper the rto value is changed to:
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* RTO = rtt + 4 * mdev
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*
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* Funny. This algorithm seems to be very broken.
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* These formulae increase RTO, when it should be decreased, increase
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* too slowly, when it should be increased quickly, decrease too quickly
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* etc. I guess in BSD RTO takes ONE value, so that it is absolutely
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* does not matter how to _calculate_ it. Seems, it was trap
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* that VJ failed to avoid. 8)
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*/
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if (srtt != 0) {
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m -= (srtt >> 3); /* m is now error in rtt est */
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srtt += m; /* rtt = 7/8 rtt + 1/8 new */
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if (m < 0) {
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m = -m; /* m is now abs(error) */
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m -= (peer->mdev_us >> 2); /* similar update on mdev */
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/* This is similar to one of Eifel findings.
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* Eifel blocks mdev updates when rtt decreases.
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* This solution is a bit different: we use finer gain
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* for mdev in this case (alpha*beta).
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* Like Eifel it also prevents growth of rto,
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* but also it limits too fast rto decreases,
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* happening in pure Eifel.
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*/
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if (m > 0)
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m >>= 3;
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} else {
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m -= (peer->mdev_us >> 2); /* similar update on mdev */
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}
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peer->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
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if (peer->mdev_us > peer->mdev_max_us) {
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peer->mdev_max_us = peer->mdev_us;
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if (peer->mdev_max_us > peer->rttvar_us)
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peer->rttvar_us = peer->mdev_max_us;
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}
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} else {
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/* no previous measure. */
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srtt = m << 3; /* take the measured time to be rtt */
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peer->mdev_us = m << 1; /* make sure rto = 3*rtt */
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peer->rttvar_us = max(peer->mdev_us, rxrpc_rto_min_us(peer));
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peer->mdev_max_us = peer->rttvar_us;
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}
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peer->srtt_us = max(1U, srtt);
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}
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/*
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* Calculate rto without backoff. This is the second half of Van Jacobson's
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* routine referred to above.
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*/
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static void rxrpc_set_rto(struct rxrpc_peer *peer)
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{
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u32 rto;
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/* 1. If rtt variance happened to be less 50msec, it is hallucination.
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* It cannot be less due to utterly erratic ACK generation made
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* at least by solaris and freebsd. "Erratic ACKs" has _nothing_
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* to do with delayed acks, because at cwnd>2 true delack timeout
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* is invisible. Actually, Linux-2.4 also generates erratic
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* ACKs in some circumstances.
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*/
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rto = __rxrpc_set_rto(peer);
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/* 2. Fixups made earlier cannot be right.
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* If we do not estimate RTO correctly without them,
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* all the algo is pure shit and should be replaced
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* with correct one. It is exactly, which we pretend to do.
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*/
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/* NOTE: clamping at RXRPC_RTO_MIN is not required, current algo
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* guarantees that rto is higher.
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*/
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peer->rto_j = rxrpc_bound_rto(rto);
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}
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static void rxrpc_ack_update_rtt(struct rxrpc_peer *peer, long rtt_us)
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{
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if (rtt_us < 0)
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return;
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//rxrpc_update_rtt_min(peer, rtt_us);
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rxrpc_rtt_estimator(peer, rtt_us);
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rxrpc_set_rto(peer);
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/* RFC6298: only reset backoff on valid RTT measurement. */
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peer->backoff = 0;
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}
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/*
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* Add RTT information to cache. This is called in softirq mode and has
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* exclusive access to the peer RTT data.
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*/
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void rxrpc_peer_add_rtt(struct rxrpc_call *call, enum rxrpc_rtt_rx_trace why,
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int rtt_slot,
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rxrpc_serial_t send_serial, rxrpc_serial_t resp_serial,
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ktime_t send_time, ktime_t resp_time)
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{
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struct rxrpc_peer *peer = call->peer;
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s64 rtt_us;
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rtt_us = ktime_to_us(ktime_sub(resp_time, send_time));
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if (rtt_us < 0)
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return;
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spin_lock(&peer->rtt_input_lock);
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rxrpc_ack_update_rtt(peer, rtt_us);
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if (peer->rtt_count < 3)
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peer->rtt_count++;
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spin_unlock(&peer->rtt_input_lock);
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trace_rxrpc_rtt_rx(call, why, rtt_slot, send_serial, resp_serial,
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peer->srtt_us >> 3, peer->rto_j);
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}
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/*
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* Get the retransmission timeout to set in jiffies, backing it off each time
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* we retransmit.
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*/
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unsigned long rxrpc_get_rto_backoff(struct rxrpc_peer *peer, bool retrans)
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{
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u64 timo_j;
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u8 backoff = READ_ONCE(peer->backoff);
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timo_j = peer->rto_j;
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timo_j <<= backoff;
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if (retrans && timo_j * 2 <= RXRPC_RTO_MAX)
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WRITE_ONCE(peer->backoff, backoff + 1);
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if (timo_j < 1)
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timo_j = 1;
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return timo_j;
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}
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void rxrpc_peer_init_rtt(struct rxrpc_peer *peer)
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{
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peer->rto_j = RXRPC_TIMEOUT_INIT;
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peer->mdev_us = jiffies_to_usecs(RXRPC_TIMEOUT_INIT);
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peer->backoff = 0;
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//minmax_reset(&peer->rtt_min, rxrpc_jiffies32, ~0U);
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}
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