| Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 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 | } |