xref: /openbmc/linux/net/sunrpc/timer.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
1 /*
2  * linux/net/sunrpc/timer.c
3  *
4  * Estimate RPC request round trip time.
5  *
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).
10  *
11  * This RTT estimator is used only for RPC over datagram protocols.
12  *
13  * Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
14  */
15 
16 #include <asm/param.h>
17 
18 #include <linux/types.h>
19 #include <linux/unistd.h>
20 
21 #include <linux/sunrpc/clnt.h>
22 #include <linux/sunrpc/xprt.h>
23 #include <linux/sunrpc/timer.h>
24 
25 #define RPC_RTO_MAX (60*HZ)
26 #define RPC_RTO_INIT (HZ/5)
27 #define RPC_RTO_MIN (HZ/10)
28 
29 void
30 rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
31 {
32 	unsigned long init = 0;
33 	unsigned i;
34 
35 	rt->timeo = timeo;
36 
37 	if (timeo > RPC_RTO_INIT)
38 		init = (timeo - RPC_RTO_INIT) << 3;
39 	for (i = 0; i < 5; i++) {
40 		rt->srtt[i] = init;
41 		rt->sdrtt[i] = RPC_RTO_INIT;
42 		rt->ntimeouts[i] = 0;
43 	}
44 }
45 
46 /*
47  * NB: When computing the smoothed RTT and standard deviation,
48  *     be careful not to produce negative intermediate results.
49  */
50 void
51 rpc_update_rtt(struct rpc_rtt *rt, unsigned timer, long m)
52 {
53 	long *srtt, *sdrtt;
54 
55 	if (timer-- == 0)
56 		return;
57 
58 	/* jiffies wrapped; ignore this one */
59 	if (m < 0)
60 		return;
61 
62 	if (m == 0)
63 		m = 1L;
64 
65 	srtt = (long *)&rt->srtt[timer];
66 	m -= *srtt >> 3;
67 	*srtt += m;
68 
69 	if (m < 0)
70 		m = -m;
71 
72 	sdrtt = (long *)&rt->sdrtt[timer];
73 	m -= *sdrtt >> 2;
74 	*sdrtt += m;
75 
76 	/* Set lower bound on the variance */
77 	if (*sdrtt < RPC_RTO_MIN)
78 		*sdrtt = RPC_RTO_MIN;
79 }
80 
81 /*
82  * Estimate rto for an nfs rpc sent via. an unreliable datagram.
83  * Use the mean and mean deviation of rtt for the appropriate type of rpc
84  * for the frequent rpcs and a default for the others.
85  * The justification for doing "other" this way is that these rpcs
86  * happen so infrequently that timer est. would probably be stale.
87  * Also, since many of these rpcs are
88  * non-idempotent, a conservative timeout is desired.
89  * getattr, lookup,
90  * read, write, commit     - A+4D
91  * other                   - timeo
92  */
93 
94 unsigned long
95 rpc_calc_rto(struct rpc_rtt *rt, unsigned timer)
96 {
97 	unsigned long res;
98 
99 	if (timer-- == 0)
100 		return rt->timeo;
101 
102 	res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
103 	if (res > RPC_RTO_MAX)
104 		res = RPC_RTO_MAX;
105 
106 	return res;
107 }
108