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1da177e4 LT |
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 | } |