105 строки
3.0 KiB
C
105 строки
3.0 KiB
C
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/*
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* Copyright (c) 2010-2011, Siberian State University of Telecommunications
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* and Information Sciences. All rights reserved.
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* Copyright (c) 2010-2011, A.V. Rzhanov Institute of Semiconductor Physics SB RAS.
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* All rights reserved.
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*
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* mpigclock.c: MPI clock synchronization.
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*
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* Copyright (C) 2011 Mikhail Kurnosov <mkurnosov@gmail.com>
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*
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* This source code is part of MPIPerf project: http://mpiperf.cpct.sibsutis.ru/index.php/Main/Documentation
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <mpi.h>
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#include "mpigclock.h"
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#include "hpctimer.h"
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#define INVALIDTIME -1.0
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#define MPIGCLOCK_RTTMIN_NOTCHANGED_MAX 100
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#define MPIGCLOCK_MSGTAG 128
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static double mpigclock_measure_offset_adaptive(MPI_Comm comm, int root, int peer, double *min_rtt);
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/*
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* mpigclock_sync_linear: Clock synchronization algorithm with O(n) steps.
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*/
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double mpigclock_sync_linear(MPI_Comm comm, int root, double *rtt)
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{
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int i, rank, commsize;
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double ret = 0;
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MPI_Comm_rank(comm, &rank);
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MPI_Comm_size(comm, &commsize);
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if (commsize < 2) {
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*rtt = 0.0;
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return 0.0;
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}
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for (i = 1; i < commsize; i++) {
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MPI_Barrier(comm);
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if (rank == root || rank == i) {
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ret = mpigclock_measure_offset_adaptive(comm, root, i, rtt);
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}
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}
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return ret;
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}
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/* mpigclock_measure_offset_adaptive: Measures clock's offset of peer. */
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static double mpigclock_measure_offset_adaptive(MPI_Comm comm, int root, int peer, double *min_rtt)
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{
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int rank, commsize, rttmin_notchanged = 0;
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double starttime, stoptime, peertime, rtt, rttmin = 1E12,
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invalidtime = INVALIDTIME, offset;
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MPI_Comm_rank(comm, &rank);
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MPI_Comm_size(comm, &commsize);
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offset = 0.0;
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for (;;) {
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if (rank != root) {
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/* Peer process */
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starttime = hpctimer_wtime();
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MPI_Send(&starttime, 1, MPI_DOUBLE, root, MPIGCLOCK_MSGTAG, comm);
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MPI_Recv(&peertime, 1, MPI_DOUBLE, root, MPIGCLOCK_MSGTAG, comm,
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MPI_STATUS_IGNORE);
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stoptime = hpctimer_wtime();
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rtt = stoptime - starttime;
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if (rtt < rttmin) {
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rttmin = rtt;
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rttmin_notchanged = 0;
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offset = peertime - rtt / 2.0 - starttime;
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} else {
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if (++rttmin_notchanged == MPIGCLOCK_RTTMIN_NOTCHANGED_MAX) {
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MPI_Send(&invalidtime, 1, MPI_DOUBLE, root, MPIGCLOCK_MSGTAG,
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comm);
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break;
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}
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}
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} else {
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/* Root process */
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MPI_Recv(&starttime, 1, MPI_DOUBLE, peer, MPIGCLOCK_MSGTAG, comm,
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MPI_STATUS_IGNORE);
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peertime = hpctimer_wtime();
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if (starttime < 0.0) {
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break;
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}
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MPI_Send(&peertime, 1, MPI_DOUBLE, peer, MPIGCLOCK_MSGTAG, comm);
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}
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} /* for */
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if( rank != root ){
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*min_rtt = rttmin;
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} else {
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rtt = 0.0;
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}
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return offset;
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}
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