net/sunrpc/timer.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * linux/net/sunrpc/timer.c
   4  *
   5  * Estimate RPC request round trip time.
   6  *
   7  * Based on packet round-trip and variance estimator algorithms described
   8  * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
   9  * and Michael J. Karels (ACM Computer Communication Review; Proceedings
  10  * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
  11  *
  12  * This RTT estimator is used only for RPC over datagram protocols.
  13  *
  14  * Copyright (C) 2002 Trond Myklebust <trond.myklebust@fys.uio.no>
  15  */
  16
  17 #include <asm/param.h>
  18
  19 #include <linux/types.h>
  20 #include <linux/unistd.h>
  21 #include <linux/module.h>
  22
  23 #include <linux/sunrpc/clnt.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 /**
  30  * rpc_init_rtt - Initialize an RPC RTT estimator context
  31  * @rt: context to initialize
  32  * @timeo: initial timeout value, in jiffies
  33  *
  34  */
  35 void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
  36 {
  37         unsigned long init = 0;
  38         unsigned int i;
  39
  40         rt->timeo = timeo;
  41
  42         if (timeo > RPC_RTO_INIT)
  43                 init = (timeo - RPC_RTO_INIT) << 3;
  44         for (i = 0; i < 5; i++) {
  45                 rt->srtt[i] = init;
  46                 rt->sdrtt[i] = RPC_RTO_INIT;
  47                 rt->ntimeouts[i] = 0;
  48         }
  49 }
  50 EXPORT_SYMBOL_GPL(rpc_init_rtt);
  51
  52 /**
  53  * rpc_update_rtt - Update an RPC RTT estimator context
  54  * @rt: context to update
  55  * @timer: timer array index (request type)
  56  * @m: recent actual RTT, in jiffies
  57  *
  58  * NB: When computing the smoothed RTT and standard deviation,
  59  *     be careful not to produce negative intermediate results.
  60  */
  61 void rpc_update_rtt(struct rpc_rtt *rt, unsigned int timer, long m)
  62 {
  63         long *srtt, *sdrtt;
  64
  65         if (timer-- == 0)
  66                 return;
  67
  68         /* jiffies wrapped; ignore this one */
  69         if (m < 0)
  70                 return;
  71
  72         if (m == 0)
  73                 m = 1L;
  74
  75         srtt = (long *)&rt->srtt[timer];
  76         m -= *srtt >> 3;
  77         *srtt += m;
  78
  79         if (m < 0)
  80                 m = -m;
  81
  82         sdrtt = (long *)&rt->sdrtt[timer];
  83         m -= *sdrtt >> 2;
  84         *sdrtt += m;
  85
  86         /* Set lower bound on the variance */
  87         if (*sdrtt < RPC_RTO_MIN)
  88                 *sdrtt = RPC_RTO_MIN;
  89 }
  90 EXPORT_SYMBOL_GPL(rpc_update_rtt);
  91
  92 /**
  93  * rpc_calc_rto - Provide an estimated timeout value
  94  * @rt: context to use for calculation
  95  * @timer: timer array index (request type)
  96  *
  97  * Estimate RTO for an NFS RPC sent via an unreliable datagram.  Use
  98  * the mean and mean deviation of RTT for the appropriate type of RPC
  99  * for frequently issued RPCs, and a fixed default for the others.
 100  *
 101  * The justification for doing "other" this way is that these RPCs
 102  * happen so infrequently that timer estimation would probably be
 103  * stale.  Also, since many of these RPCs are non-idempotent, a
 104  * conservative timeout is desired.
 105  *
 106  * getattr, lookup,
 107  * read, write, commit     - A+4D
 108  * other                   - timeo
 109  */
 110 unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned int timer)
 111 {
 112         unsigned long res;
 113
 114         if (timer-- == 0)
 115                 return rt->timeo;
 116
 117         res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
 118         if (res > RPC_RTO_MAX)
 119                 res = RPC_RTO_MAX;
 120
 121         return res;
 122 }
 123 EXPORT_SYMBOL_GPL(rpc_calc_rto);