net/sunrpc/timer.c

1 // SPDX-License-Identifier: GPL-2.0-only
5  * Estimate RPC request round trip time.
7  * Based on packet round-trip and variance estimator algorithms described
12  * This RTT estimator is used only for RPC over datagram protocols.
30  * rpc_init_rtt - Initialize an RPC RTT estimator context
40 	rt->timeo = timeo;  in rpc_init_rtt()
42 	if (timeo > RPC_RTO_INIT)  in rpc_init_rtt()
43 		init = (timeo - RPC_RTO_INIT) << 3;  in rpc_init_rtt()
45 		rt->srtt[i] = init;  in rpc_init_rtt()
46 		rt->sdrtt[i] = RPC_RTO_INIT;  in rpc_init_rtt()
47 		rt->ntimeouts[i] = 0;  in rpc_init_rtt()
53  * rpc_update_rtt - Update an RPC RTT estimator context
65 	if (timer-- == 0)  in rpc_update_rtt()
69 	if (m < 0)  in rpc_update_rtt()
72 	if (m == 0)  in rpc_update_rtt()
75 	srtt = (long *)&rt->srtt[timer];  in rpc_update_rtt()
76 	m -= *srtt >> 3;  in rpc_update_rtt()
79 	if (m < 0)  in rpc_update_rtt()
80 		m = -m;  in rpc_update_rtt()
82 	sdrtt = (long *)&rt->sdrtt[timer];  in rpc_update_rtt()
83 	m -= *sdrtt >> 2;  in rpc_update_rtt()
87 	if (*sdrtt < RPC_RTO_MIN)  in rpc_update_rtt()
93  * rpc_calc_rto - Provide an estimated timeout value
97  * Estimate RTO for an NFS RPC sent via an unreliable datagram.  Use
98  * the mean and mean deviation of RTT for the appropriate type of RPC
103  * stale.  Also, since many of these RPCs are non-idempotent, a
107  * read, write, commit     - A+4D
108  * other                   - timeo
114 	if (timer-- == 0)  in rpc_calc_rto()
115 		return rt->timeo;  in rpc_calc_rto()
117 	res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];  in rpc_calc_rto()
118 	if (res > RPC_RTO_MAX)  in rpc_calc_rto()