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
  23 #define RPC_RTO_MAX (60*HZ)
  24 #define RPC_RTO_INIT (HZ/5)
  25 #define RPC_RTO_MIN (HZ/10)
  26
  27 void
  28 rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
  29 {
  30         unsigned long init = 0;
  31         unsigned i;
  32
  33         rt->timeo = timeo;
  34
  35         if (timeo > RPC_RTO_INIT)
  36                 init = (timeo - RPC_RTO_INIT) << 3;
  37         for (i = 0; i < 5; i++) {
  38                 rt->srtt[i] = init;
  39                 rt->sdrtt[i] = RPC_RTO_INIT;
  40                 rt->ntimeouts[i] = 0;
  41         }
  42 }
  43
  44 /*
  45  * NB: When computing the smoothed RTT and standard deviation,
  46  *     be careful not to produce negative intermediate results.
  47  */
  48 void
  49 rpc_update_rtt(struct rpc_rtt *rt, unsigned timer, long m)
  50 {
  51         long *srtt, *sdrtt;
  52
  53         if (timer-- == 0)
  54                 return;
  55
  56         /* jiffies wrapped; ignore this one */
  57         if (m < 0)
  58                 return;
  59
  60         if (m == 0)
  61                 m = 1L;
  62
  63         srtt = (long *)&rt->srtt[timer];
  64         m -= *srtt >> 3;
  65         *srtt += m;
  66
  67         if (m < 0)
  68                 m = -m;
  69
  70         sdrtt = (long *)&rt->sdrtt[timer];
  71         m -= *sdrtt >> 2;
  72         *sdrtt += m;
  73
  74         /* Set lower bound on the variance */
  75         if (*sdrtt < RPC_RTO_MIN)
  76                 *sdrtt = RPC_RTO_MIN;
  77 }
  78
  79 /*
  80  * Estimate rto for an nfs rpc sent via. an unreliable datagram.
  81  * Use the mean and mean deviation of rtt for the appropriate type of rpc
  82  * for the frequent rpcs and a default for the others.
  83  * The justification for doing "other" this way is that these rpcs
  84  * happen so infrequently that timer est. would probably be stale.
  85  * Also, since many of these rpcs are
  86  * non-idempotent, a conservative timeout is desired.
  87  * getattr, lookup,
  88  * read, write, commit     - A+4D
  89  * other                   - timeo
  90  */
  91
  92 unsigned long
  93 rpc_calc_rto(struct rpc_rtt *rt, unsigned timer)
  94 {
  95         unsigned long res;
  96
  97         if (timer-- == 0)
  98                 return rt->timeo;
  99
 100         res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
 101         if (res > RPC_RTO_MAX)
 102                 res = RPC_RTO_MAX;
 103
 104         return res;
 105 }