Author: jhb
Date: Wed Sep 3 17:26:46 2014
New Revision: 271044
URL: http://svnweb.freebsd.org/changeset/base/271044
Log:
Import a hackish tool I use to examine the skew of the TSC across
CPUs in a system. The tool queries the kernel for its set of CPUs
and compares TSC values on each of the additional CPUs to the first
CPU in turn. It then outputs a table of simple statistics.
Added:
head/tools/tools/tscdrift/
head/tools/tools/tscdrift/Makefile (contents, props changed)
head/tools/tools/tscdrift/tscdrift.c (contents, props changed)
Added: head/tools/tools/tscdrift/Makefile
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ head/tools/tools/tscdrift/Makefile Wed Sep 3 17:26:46 2014
(r271044)
@@ -0,0 +1,10 @@
+# $FreeBSD$
+
+PROG= tscdrift
+MAN=
+WARNS?= 6
+
+LDADD= -lpthread -lm
+DPADD= ${LIBPTHREAD} ${LIBM}
+
+.include <bsd.prog.mk>
Added: head/tools/tools/tscdrift/tscdrift.c
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ head/tools/tools/tscdrift/tscdrift.c Wed Sep 3 17:26:46 2014
(r271044)
@@ -0,0 +1,193 @@
+/*-
+ * Copyright (c) 2014 Advanced Computing Technologies LLC
+ * Written by: John H. Baldwin <j...@freebsd.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/cpuset.h>
+#include <machine/atomic.h>
+#include <machine/cpu.h>
+#include <machine/cpufunc.h>
+#include <assert.h>
+#include <err.h>
+#include <errno.h>
+#include <math.h>
+#include <pthread.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#define barrier() __asm __volatile("" ::: "memory")
+
+#define TESTS 1024
+
+static volatile int gate;
+static volatile uint64_t thread_tsc;
+
+/* Bind the current thread to the specified CPU. */
+static void
+bind_cpu(int cpu)
+{
+ cpuset_t set;
+
+ CPU_ZERO(&set);
+ CPU_SET(cpu, &set);
+ if (cpuset_setaffinity(CPU_LEVEL_WHICH, CPU_WHICH_TID, -1, sizeof(set),
+ &set) < 0)
+ err(1, "cpuset_setaffinity(%d)", cpu);
+}
+
+static void *
+thread_main(void *arg)
+{
+ int cpu, i;
+
+ cpu = (intptr_t)arg;
+ bind_cpu(cpu);
+ for (i = 0; i < TESTS; i++) {
+ gate = 1;
+ while (gate == 1)
+ cpu_spinwait();
+ barrier();
+
+ __asm __volatile("lfence");
+ thread_tsc = rdtsc();
+
+ barrier();
+ gate = 3;
+ while (gate == 3)
+ cpu_spinwait();
+ }
+ return (NULL);
+}
+
+int
+main(int ac __unused, char **av __unused)
+{
+ cpuset_t all_cpus;
+ int64_t **skew, *aveskew, *minskew, *maxskew;
+ float *stddev;
+ double sumsq;
+ pthread_t child;
+ uint64_t tsc;
+ int *cpus;
+ int error, i, j, ncpu;
+
+ /*
+ * Find all the CPUs this program is eligible to run on and use
+ * this as our global set. This means you can use cpuset to
+ * restrict this program to only run on a subset of CPUs.
+ */
+ if (cpuset_getaffinity(CPU_LEVEL_WHICH, CPU_WHICH_PID, -1,
+ sizeof(all_cpus), &all_cpus) < 0)
+ err(1, "cpuset_getaffinity");
+ for (ncpu = 0, i = 0; i < CPU_SETSIZE; i++) {
+ if (CPU_ISSET(i, &all_cpus))
+ ncpu++;
+ }
+ if (ncpu < 2)
+ errx(1, "Only one available CPU");
+ cpus = calloc(ncpu, sizeof(*cpus));
+ skew = calloc(ncpu, sizeof(*skew));
+ for (i = 0; i < ncpu; i++)
+ skew[i] = calloc(TESTS, sizeof(*skew[i]));
+ for (i = 0, j = 0; i < CPU_SETSIZE; i++)
+ if (CPU_ISSET(i, &all_cpus)) {
+ assert(j < ncpu);
+ cpus[j] = i;
+ j++;
+ }
+
+ /*
+ * We bind this thread to the first CPU and then bind all the
+ * other threads to other CPUs in turn saving TESTS counts of
+ * skew calculations.
+ */
+ bind_cpu(cpus[0]);
+ for (i = 1; i < ncpu; i++) {
+ error = pthread_create(&child, NULL, thread_main,
+ (void *)(intptr_t)cpus[i]);
+ if (error)
+ errc(1, error, "pthread_create");
+
+ for (j = 0; j < TESTS; j++) {
+ while (gate != 1)
+ cpu_spinwait();
+ gate = 2;
+ barrier();
+
+ tsc = rdtsc();
+
+ barrier();
+ while (gate != 3)
+ cpu_spinwait();
+ gate = 4;
+
+ skew[i][j] = thread_tsc - tsc;
+ }
+
+ error = pthread_join(child, NULL);
+ if (error)
+ errc(1, error, "pthread_join");
+ }
+
+ /*
+ * Compute average skew for each CPU and output a summary of
+ * the results.
+ */
+ aveskew = calloc(ncpu, sizeof(*aveskew));
+ minskew = calloc(ncpu, sizeof(*minskew));
+ maxskew = calloc(ncpu, sizeof(*maxskew));
+ stddev = calloc(ncpu, sizeof(*stddev));
+ stddev[0] = 0.0;
+ for (i = 1; i < ncpu; i++) {
+ sumsq = 0;
+ minskew[i] = maxskew[i] = skew[i][0];
+ for (j = 0; j < TESTS; j++) {
+ aveskew[i] += skew[i][j];
+ if (skew[i][j] < minskew[i])
+ minskew[i] = skew[i][j];
+ if (skew[i][j] > maxskew[i])
+ maxskew[i] = skew[i][j];
+ sumsq += (skew[i][j] * skew[i][j]);
+ }
+ aveskew[i] /= TESTS;
+ sumsq /= TESTS;
+ sumsq -= aveskew[i] * aveskew[i];
+ stddev[i] = sqrt(sumsq);
+ }
+
+ printf("CPU | TSC skew (min/avg/max/stddev)\n");
+ printf("----+------------------------------\n");
+ for (i = 0; i < ncpu; i++)
+ printf("%3d | %5jd %5jd %5jd %6.3f\n", cpus[i],
+ (intmax_t)minskew[i], (intmax_t)aveskew[i],
+ (intmax_t)maxskew[i], stddev[i]);
+ return (0);
+}
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