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 23 #define RPC_RTO_MAX (60*HZ) 24 #define RPC_RTO_INIT (HZ/5) 25 #define RPC_RTO_MIN (HZ/10) 26 27 void 28 rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo) 29 { 30 unsigned long init = 0; 31 unsigned i; 32 33 rt->timeo = timeo; 34 35 if (timeo > RPC_RTO_INIT) 36 init = (timeo - RPC_RTO_INIT) << 3; 37 for (i = 0; i < 5; i++) { 38 rt->srtt[i] = init; 39 rt->sdrtt[i] = RPC_RTO_INIT; 40 rt->ntimeouts[i] = 0; 41 } 42 } 43 44 /* 45 * NB: When computing the smoothed RTT and standard deviation, 46 * be careful not to produce negative intermediate results. 47 */ 48 void 49 rpc_update_rtt(struct rpc_rtt *rt, unsigned timer, long m) 50 { 51 long *srtt, *sdrtt; 52 53 if (timer-- == 0) 54 return; 55 56 /* jiffies wrapped; ignore this one */ 57 if (m < 0) 58 return; 59 60 if (m == 0) 61 m = 1L; 62 63 srtt = (long *)&rt->srtt[timer]; 64 m -= *srtt >> 3; 65 *srtt += m; 66 67 if (m < 0) 68 m = -m; 69 70 sdrtt = (long *)&rt->sdrtt[timer]; 71 m -= *sdrtt >> 2; 72 *sdrtt += m; 73 74 /* Set lower bound on the variance */ 75 if (*sdrtt < RPC_RTO_MIN) 76 *sdrtt = RPC_RTO_MIN; 77 } 78 79 /* 80 * Estimate rto for an nfs rpc sent via. an unreliable datagram. 81 * Use the mean and mean deviation of rtt for the appropriate type of rpc 82 * for the frequent rpcs and a default for the others. 83 * The justification for doing "other" this way is that these rpcs 84 * happen so infrequently that timer est. would probably be stale. 85 * Also, since many of these rpcs are 86 * non-idempotent, a conservative timeout is desired. 87 * getattr, lookup, 88 * read, write, commit - A+4D 89 * other - timeo 90 */ 91 92 unsigned long 93 rpc_calc_rto(struct rpc_rtt *rt, unsigned timer) 94 { 95 unsigned long res; 96 97 if (timer-- == 0) 98 return rt->timeo; 99 100 res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer]; 101 if (res > RPC_RTO_MAX) 102 res = RPC_RTO_MAX; 103 104 return res; 105 } 106