ovni/ovnisync.c

#include <limits.h>
#include <time.h>
#include <stdio.h>
#include <mpi.h>
#include <stdlib.h>
#include <math.h>
#include <unistd.h>
#include <assert.h>

#include "ovni.h"

const char progname[] = "ovnisync";

struct offset {
	/* All in nanoseconds */
	double delta_mean;
	double delta_median;
	double delta_var;
	double delta_std;

	/* The value selected for the offset */
	int64_t offset;

	/* In seconds */
	double wall_t0;
	double wall_t1;

	char hostname[OVNI_MAX_HOSTNAME];
	int rank;

	int nsamples;

	/* Flexible array */
	double clock_sample[];
};

struct offset_table {
	int nprocs;
	struct offset *_offset;
	struct offset **offset;
};

struct options {
	int nsamples;
	int ndrift_samples;
	int drift_wait; /* in seconds */
	int verbose;
};

static double
get_time(clockid_t clock, int use_ns)
{
	struct timespec tv;
	if(clock_gettime(clock, &tv) != 0)
	{
		perror("clock_gettime failed");
		exit(EXIT_FAILURE);
	}

	if(use_ns)
		return (double)(tv.tv_sec) * 1.0e9 +
			(double)tv.tv_nsec;

	return (double)(tv.tv_sec) +
		(double)tv.tv_nsec * 1.0e-9;
}

static int
cmp_double(const void *pa, const void *pb)
{
	double a, b;

	a = *(const double *) pa;
	b = *(const double *) pb;

	if(a < b)
		return -1;
	else if(a > b)
		return 1;
	else
		return 0;
}

void
usage(int argc, char *argv[])
{
	fprintf(stderr, "%s: clock synchronization utility\n", progname);
	fprintf(stderr, "\n");
	fprintf(stderr, "Usage: %s [-d ndrift_samples] [-v] [-n nsamples] [-w drift_delay]\n",
			progname);
	exit(EXIT_FAILURE);
}

void
parse_options(struct options *options, int argc, char *argv[])
{
	int opt;

	/* Default options */
	options->ndrift_samples = 1;
	options->nsamples = 100;
	options->verbose = 0;
	options->drift_wait = 5;

	while ((opt = getopt(argc, argv, "d:vn:w:")) != -1) {
		switch (opt) {
			case 'd':
				options->ndrift_samples = atoi(optarg);
				break;
			case 'w':
				options->drift_wait = atoi(optarg);
				break;
			case 'v':
				options->verbose = 1;
				break;
			case 'n':
				options->nsamples = atoi(optarg);
				break;
			default: /* '?' */
				usage(argc, argv);
		}
	}

	if (optind < argc)
	{
		fprintf(stderr, "error: unexpected extra arguments\n");
		exit(EXIT_FAILURE);
	}
}

void
get_clock_samples(struct offset *offset, int nsamples)
{
	int i;

	/* Keep the wall time as well */
	offset->wall_t0 = get_time(CLOCK_REALTIME, 0);

	offset->nsamples = nsamples;

	for(i=0; i<nsamples; i++)
	{
		MPI_Barrier(MPI_COMM_WORLD);
		offset->clock_sample[i] = get_time(CLOCK_MONOTONIC, 1);
	}

	offset->wall_t1 = get_time(CLOCK_REALTIME, 0);
}

void
fill_offset(struct offset *offset, int nsamples)
{
	int warmup_nsamples;

	/* Identify the rank */
	MPI_Comm_rank(MPI_COMM_WORLD, &offset->rank);

	/* Fill the host name */
	if(gethostname(offset->hostname, OVNI_MAX_HOSTNAME) != 0)
	{
		perror("gethostname");
		exit(EXIT_FAILURE);
	}

	//printf("rank=%d hostname=%s\n", offset->rank, offset->hostname);

	/* Warm up iterations */
	warmup_nsamples = nsamples >= 20 ? 20 : nsamples;
	get_clock_samples(offset, warmup_nsamples);

	get_clock_samples(offset, nsamples);
}

void
offset_compute_delta(struct offset *ref, struct offset *cur, int nsamples)
{
	int i;
	double *delta;

	delta = malloc(sizeof(double) * nsamples);

	if(delta == NULL)
	{
		perror("malloc");
		exit(EXIT_FAILURE);
	}

	for(i=0; i<nsamples; i++)
	{
		delta[i] = ref->clock_sample[i] - cur->clock_sample[i];
		//printf("rank=%d  sample=%d  delta=%f  ref=%f  cur=%f\n",
		//		cur->rank, i, delta[i], ref->clock_sample[i], cur->clock_sample[i]);
	}

	qsort(delta, nsamples, sizeof(double), cmp_double);

	cur->delta_median = delta[nsamples / 2];

	for(cur->delta_mean=0, i=0; i<nsamples; i++)
		cur->delta_mean += delta[i];

	cur->delta_mean /= nsamples;

	for(cur->delta_var=0, i=0; i<nsamples; i++)
		cur->delta_var += (delta[i] - cur->delta_mean) *
			(delta[i] - cur->delta_mean);

	cur->delta_var /= (double) (nsamples - 1);
	cur->delta_std = sqrt(cur->delta_var);

	/* The median is the selected metric for the offset */
	cur->offset = (int64_t) cur->delta_median;

	free(delta);
}

size_t
offset_size(int nsamples)
{
	return sizeof(struct offset) + sizeof(double) * nsamples;
}

struct offset *
table_get_offset(struct offset_table *table, int i, int nsamples)
{
	char *p;

	p = (char *) table->_offset;
	p += i * offset_size(nsamples);

	return (struct offset *) p;
}

struct offset_table *
build_offset_table(int nsamples, int rank)
{
	int i;
	struct offset_table *table = NULL;
	struct offset *offset = NULL;
	void *sendbuf;

	/* The rank 0 must build the table */
	if(rank == 0)
	{
		table = malloc(sizeof(*table));

		if(table == NULL)
		{
			perror("malloc");
			exit(EXIT_FAILURE);
		}

		MPI_Comm_size(MPI_COMM_WORLD, &table->nprocs);

		table->_offset = calloc(table->nprocs, offset_size(nsamples));

		if(table->_offset == NULL)
		{
			perror("malloc");
			exit(EXIT_FAILURE);
		}

		table->offset = malloc(sizeof(struct offset *) *
				table->nprocs);

		if(table->offset == NULL)
		{
			perror("malloc");
			exit(EXIT_FAILURE);
		}

		for(i=0; i<table->nprocs; i++)
			table->offset[i] = table_get_offset(table, i, nsamples);

		offset = table->offset[0];
	}
	else
	{
		/* Otherwise just allocate one offset */
		offset = calloc(1, offset_size(nsamples));

		if(offset == NULL)
		{
			perror("malloc");
			exit(EXIT_FAILURE);
		}

		table = NULL;
	}

	/* Each rank fills its own offset */
	fill_offset(offset, nsamples);

	sendbuf = rank == 0 ? MPI_IN_PLACE : offset;

	/* Then collect all the offsets into the rank 0 */
	MPI_Gather(sendbuf, offset_size(nsamples), MPI_CHAR,
			offset, offset_size(nsamples), MPI_CHAR,
			0, MPI_COMM_WORLD);

	/* Finish the offsets by computing the deltas on rank 0 */
	if(rank == 0)
	{
		for(i=0; i<table->nprocs; i++)
		{
			offset_compute_delta(offset, table->offset[i],
					nsamples);
		}
	}

	/* Cleanup for non-zero ranks */
	if(rank != 0)
		free(offset);

	return table;
}

void
print_drift_header(struct offset_table *table)
{
	int i;
	//char buf[64];

	printf("%-20s", "wallclock");

	for(i=0; i<table->nprocs; i++)
	{
		//sprintf(buf, "rank%d", i);
		printf(" %-20s", table->offset[i]->hostname);
	}

	printf("\n");
}

void
print_drift_row(struct offset_table *table)
{
	int i;
	char buf[64];

	printf("%-20f", table->offset[0]->wall_t1);

	for(i=0; i<table->nprocs; i++)
		printf(" %-20ld", table->offset[i]->offset);

	printf("\n");
}

void
print_table_detailed(struct offset_table *table)
{
	int i;
	struct offset *offset;

	printf("%-10s %-20s %-20s %-20s %-20s\n", "rank", "hostname", "offset_median", "offset_mean", "offset_std");
	for(i=0; i<table->nprocs; i++)
	{
		offset = table->offset[i];
		printf("%-10d %-20s %-20ld %-20f %-20f\n",
				i, offset->hostname, offset->offset,
				offset->delta_mean, offset->delta_std);
	}
}

void
do_work(struct options *options, int rank)
{
	int drift_mode;
	int i;
	struct offset_table *table;

	drift_mode = options->ndrift_samples > 1 ? 1 : 0;

	for(i=0; i<options->ndrift_samples; i++)
	{
		table = build_offset_table(options->nsamples, rank);

		if(rank == 0)
		{
			if(drift_mode)
			{
				if(i == 0)
					print_drift_header(table);

				print_drift_row(table);
			}
			else
			{
				print_table_detailed(table);
			}

			free(table->_offset);
			free(table->offset);
			free(table);
		}

		if(drift_mode)
			usleep(options->drift_wait * 1000 * 1000);
	}
}

int
main(int argc, char *argv[])
{
	int rank;
	struct options options;

	MPI_Init(&argc, &argv);

	MPI_Comm_rank(MPI_COMM_WORLD, &rank);

	parse_options(&options, argc, argv);

	do_work(&options, rank);

	MPI_Finalize();

	return 0;
}