/* * linux/net/sunrpc/timer.c * * Estimate RPC request round trip time. * * Based on packet round-trip and variance estimator algorithms described * in appendix A of "Congestion Avoidance and Control" by Van Jacobson * and Michael J. Karels (ACM Computer Communication Review; Proceedings * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988). * * This RTT estimator is used only for RPC over datagram protocols. * * Copyright (C) 2002 Trond Myklebust */ #include #include #include #include #include #define RPC_RTO_MAX (60*HZ) #define RPC_RTO_INIT (HZ/5) #define RPC_RTO_MIN (HZ/10) /** * rpc_init_rtt - Initialize an RPC RTT estimator context * @rt: context to initialize * @timeo: initial timeout value, in jiffies * */ void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo) { unsigned long init = 0; unsigned int i; rt->timeo = timeo; if (timeo > RPC_RTO_INIT) init = (timeo - RPC_RTO_INIT) << 3; for (i = 0; i < 5; i++) { rt->srtt[i] = init; rt->sdrtt[i] = RPC_RTO_INIT; rt->ntimeouts[i] = 0; } } EXPORT_SYMBOL_GPL(rpc_init_rtt); /** * rpc_update_rtt - Update an RPC RTT estimator context * @rt: context to update * @timer: timer array index (request type) * @m: recent actual RTT, in jiffies * * NB: When computing the smoothed RTT and standard deviation, * be careful not to produce negative intermediate results. */ void rpc_update_rtt(struct rpc_rtt *rt, unsigned int timer, long m) { long *srtt, *sdrtt; if (timer-- == 0) return; /* jiffies wrapped; ignore this one */ if (m < 0) return; if (m == 0) m = 1L; srtt = (long *)&rt->srtt[timer]; m -= *srtt >> 3; *srtt += m; if (m < 0) m = -m; sdrtt = (long *)&rt->sdrtt[timer]; m -= *sdrtt >> 2; *sdrtt += m; /* Set lower bound on the variance */ if (*sdrtt < RPC_RTO_MIN) *sdrtt = RPC_RTO_MIN; } EXPORT_SYMBOL_GPL(rpc_update_rtt); /** * rpc_calc_rto - Provide an estimated timeout value * @rt: context to use for calculation * @timer: timer array index (request type) * * Estimate RTO for an NFS RPC sent via an unreliable datagram. Use * the mean and mean deviation of RTT for the appropriate type of RPC * for frequently issued RPCs, and a fixed default for the others. * * The justification for doing "other" this way is that these RPCs * happen so infrequently that timer estimation would probably be * stale. Also, since many of these RPCs are non-idempotent, a * conservative timeout is desired. * * getattr, lookup, * read, write, commit - A+4D * other - timeo */ unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned int timer) { unsigned long res; if (timer-- == 0) return rt->timeo; res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer]; if (res > RPC_RTO_MAX) res = RPC_RTO_MAX; return res; } EXPORT_SYMBOL_GPL(rpc_calc_rto); >/net/6lowpan/nhc_hop.c

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