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diff --git a/share/examples/hwpmc/overhead.c b/share/examples/hwpmc/overhead.c
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+++ b/share/examples/hwpmc/overhead.c
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+/*-
+ * Copyright (c) 2014, Neville-Neil Consulting
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * Author: George V. Neville-Neil
+ *
+ */
+
+/*
+ * Calculate the time overhead of starting, stopping, and recording
+ * pmc counters.
+ *
+ * The only argument is a counter name, such as "instruction-retired"
+ * which is CPU dependent and can be found with pmmcontrol(8) using
+ * pmccontrol -L.
+ *
+ * The start, stop, read and write operations are timed using the
+ * rdtsc() macro which reads the Time Stamp Counter on the CPU.
+ */
+
+#include <stdio.h>
+#include <err.h>
+#include <sysexits.h>
+#include <sys/types.h>
+#include <machine/cpufunc.h>
+#include <pmc.h>
+
+int
+main(int argc, char **argv)
+{
+	pmc_id_t pmcid;
+	pmc_value_t read_value;
+	pmc_value_t read_clear_value;
+	uint64_t tsc1, write_cyc, start_cyc, read_cyc, stop_cyc;
+	char *counter_name;
+	
+	if (argc != 2)
+		err(EX_USAGE, "counter-name required");
+
+	counter_name = argv[1];
+	
+	if (pmc_init() != 0)
+		err(EX_OSERR, "hwpmc(4) not loaded, kldload or update your kernel");
+
+	if (pmc_allocate(counter_name, PMC_MODE_SC, 0, 0, &pmcid, 64*1024) < 0)
+		err(EX_OSERR, "failed to allocate %s as a system counter in counting mode",
+		    counter_name);
+
+	tsc1 = rdtsc();
+	if (pmc_write(pmcid, 0) < 0)
+		err(EX_OSERR, "failed to zero counter %s", counter_name);
+	write_cyc = rdtsc() - tsc1;
+
+	tsc1 = rdtsc();
+	if (pmc_start(pmcid) < 0)
+		err(EX_OSERR, "failed to start counter %s", counter_name);
+	start_cyc = rdtsc() - tsc1;
+
+	tsc1 = rdtsc();
+	if (pmc_read(pmcid, &read_value) < 0)
+		err(EX_OSERR, "failed to read counter %s", counter_name);
+	read_cyc = rdtsc() - tsc1;
+
+	tsc1 = rdtsc();
+	if (pmc_stop(pmcid) < 0)
+		err(EX_OSERR, "failed to stop counter %s", counter_name);
+	stop_cyc = rdtsc() - tsc1;
+	
+	if (pmc_rw(pmcid, 0, &read_clear_value))
+		err(EX_OSERR, "failed to read and zero %s", counter_name);
+
+	if (pmc_release(pmcid) < 0)
+		err(EX_OSERR, "failed to release %s as a system counter in counting mode",
+		    counter_name);
+
+	printf("Counter %s, read value %ld, read/clear value %ld\n",
+	    counter_name, read_value, read_clear_value);
+	printf("Cycles to start: %ld\tstop: %ld\tread: %ld\twrite: %ld\n",
+	    start_cyc, stop_cyc, read_cyc, stop_cyc);
+
+	return(0);
+}
+