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