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 #include <linux/module.h> 21 22 #include <linux/sunrpc/clnt.h> 23 24 #define RPC_RTO_MAX (60*HZ) 25 #define RPC_RTO_INIT (HZ/5) 26 #define RPC_RTO_MIN (HZ/10) 27 28 void 29 rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo) 30 { 31 unsigned long init = 0; 32 unsigned i; 33 34 rt->timeo = timeo; 35 36 if (timeo > RPC_RTO_INIT) 37 init = (timeo - RPC_RTO_INIT) << 3; 38 for (i = 0; i < 5; i++) { 39 rt->srtt[i] = init; 40 rt->sdrtt[i] = RPC_RTO_INIT; 41 rt->ntimeouts[i] = 0; 42 } 43 } 44 EXPORT_SYMBOL_GPL(rpc_init_rtt); 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 EXPORT_SYMBOL_GPL(rpc_update_rtt); 81 82 /* 83 * Estimate rto for an nfs rpc sent via. an unreliable datagram. 84 * Use the mean and mean deviation of rtt for the appropriate type of rpc 85 * for the frequent rpcs and a default for the others. 86 * The justification for doing "other" this way is that these rpcs 87 * happen so infrequently that timer est. would probably be stale. 88 * Also, since many of these rpcs are 89 * non-idempotent, a conservative timeout is desired. 90 * getattr, lookup, 91 * read, write, commit - A+4D 92 * other - timeo 93 */ 94 95 unsigned long 96 rpc_calc_rto(struct rpc_rtt *rt, unsigned timer) 97 { 98 unsigned long res; 99 100 if (timer-- == 0) 101 return rt->timeo; 102 103 res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer]; 104 if (res > RPC_RTO_MAX) 105 res = RPC_RTO_MAX; 106 107 return res; 108 } 109 EXPORT_SYMBOL_GPL(rpc_calc_rto); 110