net/sunrpc/timer.c

   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 /**
  29  * rpc_init_rtt - Initialize an RPC RTT estimator context
  30  * @rt: context to initialize
  31  * @timeo: initial timeout value, in jiffies
  32  *
  33  */
  34 void rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
  35 {
  36         unsigned long init = 0;
  37         unsigned i;
  38
  39         rt->timeo = timeo;
  40
  41         if (timeo > RPC_RTO_INIT)
  42                 init = (timeo - RPC_RTO_INIT) << 3;
  43         for (i = 0; i < 5; i++) {
  44                 rt->srtt[i] = init;
  45                 rt->sdrtt[i] = RPC_RTO_INIT;
  46                 rt->ntimeouts[i] = 0;
  47         }
  48 }
  49 EXPORT_SYMBOL_GPL(rpc_init_rtt);
  50
  51 /**
  52  * rpc_update_rtt - Update an RPC RTT estimator context
  53  * @rt: context to update
  54  * @timer: timer array index (request type)
  55  * @m: recent actual RTT, in jiffies
  56  *
  57  * NB: When computing the smoothed RTT and standard deviation,
  58  *     be careful not to produce negative intermediate results.
  59  */
  60 void rpc_update_rtt(struct rpc_rtt *rt, unsigned timer, long m)
  61 {
  62         long *srtt, *sdrtt;
  63
  64         if (timer-- == 0)
  65                 return;
  66
  67         /* jiffies wrapped; ignore this one */
  68         if (m < 0)
  69                 return;
  70
  71         if (m == 0)
  72                 m = 1L;
  73
  74         srtt = (long *)&rt->srtt[timer];
  75         m -= *srtt >> 3;
  76         *srtt += m;
  77
  78         if (m < 0)
  79                 m = -m;
  80
  81         sdrtt = (long *)&rt->sdrtt[timer];
  82         m -= *sdrtt >> 2;
  83         *sdrtt += m;
  84
  85         /* Set lower bound on the variance */
  86         if (*sdrtt < RPC_RTO_MIN)
  87                 *sdrtt = RPC_RTO_MIN;
  88 }
  89 EXPORT_SYMBOL_GPL(rpc_update_rtt);
  90
  91 /**
  92  * rpc_calc_rto - Provide an estimated timeout value
  93  * @rt: context to use for calculation
  94  * @timer: timer array index (request type)
  95  *
  96  * Estimate RTO for an NFS RPC sent via an unreliable datagram.  Use
  97  * the mean and mean deviation of RTT for the appropriate type of RPC
  98  * for frequently issued RPCs, and a fixed default for the others.
  99  *
 100  * The justification for doing "other" this way is that these RPCs
 101  * happen so infrequently that timer estimation would probably be
 102  * stale.  Also, since many of these RPCs are non-idempotent, a
 103  * conservative timeout is desired.
 104  *
 105  * getattr, lookup,
 106  * read, write, commit     - A+4D
 107  * other                   - timeo
 108  */
 109 unsigned long rpc_calc_rto(struct rpc_rtt *rt, unsigned timer)
 110 {
 111         unsigned long res;
 112
 113         if (timer-- == 0)
 114                 return rt->timeo;
 115
 116         res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
 117         if (res > RPC_RTO_MAX)
 118                 res = RPC_RTO_MAX;
 119
 120         return res;
 121 }
 122 EXPORT_SYMBOL_GPL(rpc_calc_rto);