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
  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 }