| 1 | |
| 2 | * linux/net/sunrpc/timer.c
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| 3 | *
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| 4 | * Estimate RPC request round trip time.
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| 5 | *
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| 6 | * Based on packet round-trip and variance estimator algorithms described
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| 7 | * in appendix A of "Congestion Avoidance and Control" by Van Jacobson
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| 8 | * and Michael J. Karels (ACM Computer Communication Review; Proceedings
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| 9 | * of the Sigcomm '88 Symposium in Stanford, CA, August, 1988).
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| 10 | *
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| 11 | * This RTT estimator is used only for RPC over datagram protocols.
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| 12 | *
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| 13 | * Copyright (C) 2002 Trond Myklebust <[email protected]>
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| 14 |
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| 15 |
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| 16 | #include <asm/param.h>
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| 17 |
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| 18 | #include <linux/types.h>
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| 19 | #include <linux/unistd.h>
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| 20 |
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| 21 | #include <linux/sunrpc/clnt.h>
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| 22 |
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| 23 | #define RPC_RTO_MAX (60*HZ)
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| 24 | #define RPC_RTO_INIT (HZ/5)
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| 25 | #define RPC_RTO_MIN (HZ/10)
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| 26 |
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| 27 | void
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| 28 | rpc_init_rtt(struct rpc_rtt *rt, unsigned long timeo)
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| 29 | {
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| 30 | unsigned long init = 0;
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| 31 | unsigned i;
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| 32 |
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| 33 | rt->timeo = timeo;
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| 34 |
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| 35 | if (timeo > RPC_RTO_INIT)
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| 36 | init = (timeo - RPC_RTO_INIT) << 3;
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| 37 | for (i = 0; i < 5; i++) {
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| 38 | rt->srtt[i] = init;
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| 39 | rt->sdrtt[i] = RPC_RTO_INIT;
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| 40 | rt->ntimeouts[i] = 0;
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| 41 | }
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| 42 | }
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| 43 |
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| 44 | |
| 45 | * NB: When computing the smoothed RTT and standard deviation,
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| 46 | * be careful not to produce negative intermediate results.
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| 47 |
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| 48 | void
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| 49 | rpc_update_rtt(struct rpc_rtt *rt, unsigned timer, long m)
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| 50 | {
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| 51 | long *srtt, *sdrtt;
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| 52 |
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| 53 | if (timer-- == 0)
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| 54 | return;
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| 55 |
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| 56 |
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| 57 | if (m < 0)
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| 58 | return;
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| 59 |
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| 60 | if (m == 0)
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| 61 | m = 1L;
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| 62 |
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| 63 | srtt = (long *)&rt->srtt[timer];
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| 64 | m -= *srtt >> 3;
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| 65 | *srtt += m;
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| 66 |
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| 67 | if (m < 0)
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| 68 | m = -m;
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| 69 |
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| 70 | sdrtt = (long *)&rt->sdrtt[timer];
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| 71 | m -= *sdrtt >> 2;
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| 72 | *sdrtt += m;
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| 73 |
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| 74 |
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| 75 | if (*sdrtt < RPC_RTO_MIN)
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| 76 | *sdrtt = RPC_RTO_MIN;
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| 77 | }
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| 78 |
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| 79 | |
| 80 | * Estimate rto for an nfs rpc sent via. an unreliable datagram.
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| 81 | * Use the mean and mean deviation of rtt for the appropriate type of rpc
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| 82 | * for the frequent rpcs and a default for the others.
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| 83 | * The justification for doing "other" this way is that these rpcs
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| 84 | * happen so infrequently that timer est. would probably be stale.
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| 85 | * Also, since many of these rpcs are
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| 86 | * non-idempotent, a conservative timeout is desired.
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| 87 | * getattr, lookup,
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| 88 | * read, write, commit - A+4D
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| 89 | * other - timeo
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| 90 |
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| 91 |
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| 92 | unsigned long
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| 93 | rpc_calc_rto(struct rpc_rtt *rt, unsigned timer)
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| 94 | {
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| 95 | unsigned long res;
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| 96 |
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| 97 | if (timer-- == 0)
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| 98 | return rt->timeo;
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| 99 |
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| 100 | res = ((rt->srtt[timer] + 7) >> 3) + rt->sdrtt[timer];
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| 101 | if (res > RPC_RTO_MAX)
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| 102 | res = RPC_RTO_MAX;
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| 103 |
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| 104 | return res;
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| 105 | }
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