]>
git.proxmox.com Git - mirror_ubuntu-focal-kernel.git/blob - net/sunrpc/timer.c
2 * linux/net/sunrpc/timer.c
4 * Estimate RPC request round trip time.
6 * Based on packet round-trip and variance estimator algorithms described
7 * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
8 * and Michael J. Karels (ACM Computer Communication Review; Proceedings
9 * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
11 * This RTT estimator is used only for RPC over datagram protocols.
13 * Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
16 #include <asm/param.h>
18 #include <linux/types.h>
19 #include <linux/unistd.h>
20 #include <linux/module.h>
22 #include <linux/sunrpc/clnt.h>
24 #define RPC_RTO_MAX (60*HZ)
25 #define RPC_RTO_INIT (HZ/5)
26 #define RPC_RTO_MIN (HZ/10)
29 * rpc_init_rtt - Initialize an RPC RTT estimator context
30 * @rt: context to initialize
31 * @timeo: initial timeout value, in jiffies
34 void rpc_init_rtt(struct rpc_rtt
*rt
, unsigned long timeo
)
36 unsigned long init
= 0;
41 if (timeo
> RPC_RTO_INIT
)
42 init
= (timeo
- RPC_RTO_INIT
) << 3;
43 for (i
= 0; i
< 5; i
++) {
45 rt
->sdrtt
[i
] = RPC_RTO_INIT
;
49 EXPORT_SYMBOL_GPL(rpc_init_rtt
);
52 * rpc_update_rtt - Update an RPC RTT estimator context
53 * @rt: context to update
54 * @timer: timer array index (request type)
55 * @m: recent actual RTT, in jiffies
57 * NB: When computing the smoothed RTT and standard deviation,
58 * be careful not to produce negative intermediate results.
60 void rpc_update_rtt(struct rpc_rtt
*rt
, unsigned int timer
, long m
)
67 /* jiffies wrapped; ignore this one */
74 srtt
= (long *)&rt
->srtt
[timer
];
81 sdrtt
= (long *)&rt
->sdrtt
[timer
];
85 /* Set lower bound on the variance */
86 if (*sdrtt
< RPC_RTO_MIN
)
89 EXPORT_SYMBOL_GPL(rpc_update_rtt
);
92 * rpc_calc_rto - Provide an estimated timeout value
93 * @rt: context to use for calculation
94 * @timer: timer array index (request type)
96 * Estimate RTO for an NFS RPC sent via an unreliable datagram. Use
97 * the mean and mean deviation of RTT for the appropriate type of RPC
98 * for frequently issued RPCs, and a fixed default for the others.
100 * The justification for doing "other" this way is that these RPCs
101 * happen so infrequently that timer estimation would probably be
102 * stale. Also, since many of these RPCs are non-idempotent, a
103 * conservative timeout is desired.
106 * read, write, commit - A+4D
109 unsigned long rpc_calc_rto(struct rpc_rtt
*rt
, unsigned int timer
)
116 res
= ((rt
->srtt
[timer
] + 7) >> 3) + rt
->sdrtt
[timer
];
117 if (res
> RPC_RTO_MAX
)
122 EXPORT_SYMBOL_GPL(rpc_calc_rto
);