1/*-
2 * Copyright (c) 2014 Hudson River Trading LLC
3 * Written by: John H. Baldwin <jhb@FreeBSD.org>
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 *    notice, this list of conditions and the following disclaimer in the
13 *    documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28#include <sys/param.h>
29#include <sys/cpuset.h>
30#include <machine/atomic.h>
31#include <machine/cpu.h>
32#include <machine/cpufunc.h>
33#include <assert.h>
34#include <err.h>
35#include <errno.h>
36#include <math.h>
37#include <pthread.h>
38#include <stdint.h>
39#include <stdlib.h>
40#include <stdio.h>
41
42#define	barrier()	__asm __volatile("" ::: "memory")
43
44#define	TESTS		1024
45
46static volatile int gate;
47static volatile uint64_t thread_tsc;
48
49/* Bind the current thread to the specified CPU. */
50static void
51bind_cpu(int cpu)
52{
53	cpuset_t set;
54
55	CPU_ZERO(&set);
56	CPU_SET(cpu, &set);
57	if (cpuset_setaffinity(CPU_LEVEL_WHICH, CPU_WHICH_TID, -1, sizeof(set),
58	    &set) < 0)
59		err(1, "cpuset_setaffinity(%d)", cpu);
60}
61
62static void *
63thread_main(void *arg)
64{
65	int cpu, i;
66
67	cpu = (intptr_t)arg;
68	bind_cpu(cpu);
69	for (i = 0; i < TESTS; i++) {
70		gate = 1;
71		while (gate == 1)
72			cpu_spinwait();
73		barrier();
74
75		__asm __volatile("lfence");
76		thread_tsc = rdtsc();
77
78		barrier();
79		gate = 3;
80		while (gate == 3)
81			cpu_spinwait();
82	}
83	return (NULL);
84}
85
86int
87main(int ac __unused, char **av __unused)
88{
89	cpuset_t all_cpus;
90	int64_t **skew, *aveskew, *minskew, *maxskew;
91	float *stddev;
92	double sumsq;
93	pthread_t child;
94	uint64_t tsc;
95	int *cpus;
96	int error, i, j, ncpu;
97
98	/*
99	 * Find all the CPUs this program is eligible to run on and use
100	 * this as our global set.  This means you can use cpuset to
101	 * restrict this program to only run on a subset of CPUs.
102	 */
103	if (cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID, -1,
104	    sizeof(all_cpus), &all_cpus) < 0)
105		err(1, "cpuset_getaffinity");
106	for (ncpu = 0, i = 0; i < CPU_SETSIZE; i++) {
107		if (CPU_ISSET(i, &all_cpus))
108			ncpu++;
109	}
110	if (ncpu < 2)
111		errx(1, "Only one available CPU");
112	cpus = calloc(ncpu, sizeof(*cpus));
113	skew = calloc(ncpu, sizeof(*skew));
114	for (i = 0; i < ncpu; i++)
115		skew[i] = calloc(TESTS, sizeof(*skew[i]));
116	for (i = 0, j = 0; i < CPU_SETSIZE; i++)
117		if (CPU_ISSET(i, &all_cpus)) {
118			assert(j < ncpu);
119			cpus[j] = i;
120			j++;
121		}
122
123	/*
124	 * We bind this thread to the first CPU and then bind all the
125	 * other threads to other CPUs in turn saving TESTS counts of
126	 * skew calculations.
127	 */
128	bind_cpu(cpus[0]);
129	for (i = 1; i < ncpu; i++) {
130		error = pthread_create(&child, NULL, thread_main,
131		    (void *)(intptr_t)cpus[i]);
132		if (error)
133			errc(1, error, "pthread_create");
134
135		for (j = 0; j < TESTS; j++) {
136			while (gate != 1)
137				cpu_spinwait();
138			gate = 2;
139			barrier();
140
141			tsc = rdtsc();
142
143			barrier();
144			while (gate != 3)
145				cpu_spinwait();
146			gate = 4;
147
148			skew[i][j] = thread_tsc - tsc;
149		}
150
151		error = pthread_join(child, NULL);
152		if (error)
153			errc(1, error, "pthread_join");
154	}
155
156	/*
157	 * Compute average skew for each CPU and output a summary of
158	 * the results.
159	 */
160	aveskew = calloc(ncpu, sizeof(*aveskew));
161	minskew = calloc(ncpu, sizeof(*minskew));
162	maxskew = calloc(ncpu, sizeof(*maxskew));
163	stddev = calloc(ncpu, sizeof(*stddev));
164	stddev[0] = 0.0;
165	for (i = 1; i < ncpu; i++) {
166		sumsq = 0;
167		minskew[i] = maxskew[i] = skew[i][0];
168		for (j = 0; j < TESTS; j++) {
169			aveskew[i] += skew[i][j];
170			if (skew[i][j] < minskew[i])
171				minskew[i] = skew[i][j];
172			if (skew[i][j] > maxskew[i])
173				maxskew[i] = skew[i][j];
174			sumsq += (skew[i][j] * skew[i][j]);
175		}
176		aveskew[i] /= TESTS;
177		sumsq /= TESTS;
178		sumsq -= aveskew[i] * aveskew[i];
179		stddev[i] = sqrt(sumsq);
180	}
181
182	printf("CPU | TSC skew (min/avg/max/stddev)\n");
183	printf("----+------------------------------\n");
184	for (i = 0; i < ncpu; i++)
185		printf("%3d | %5jd %5jd %5jd   %6.3f\n", cpus[i],
186		    (intmax_t)minskew[i], (intmax_t)aveskew[i],
187		    (intmax_t)maxskew[i], stddev[i]);
188	return (0);
189}
190