Skip to main content

Browse the archive

https://github.com/torvalds/linux
05 April 2024, 19:05:47 UTC
Revision d4794f25f122aa1a8a073be51112edaa723ffff4 authored by Yazen Ghannam on 25 March 2019, 17:32:42 UTC, committed by Len Brown on 31 August 2019, 18:48:34 UTC 
tools/power turbostat: Make interval calculation per thread to reduce jitter
 
Turbostat currently normalizes TSC and other values by dividing by an
interval. This interval is the delta between the start of one global
(all counters on all CPUs) sampling and the start of another. However,
this introduces a lot of jitter into the data.

In order to reduce jitter, the interval calculation should be based on
timestamps taken per thread and close to the start of the thread's
sampling.

Define a per thread time value to hold the delta between samples taken
on the thread.

Use the timestamp taken at the beginning of sampling to calculate the
delta.

Move the thread's beginning timestamp to after the CPU migration to
avoid jitter due to the migration.

Use the global time delta for the average time delta.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Len Brown <len.brown@intel.com>
1 parent d743dae
Raw File
Tip revision: d4794f25f122aa1a8a073be51112edaa723ffff4 authored by Yazen Ghannam on 25 March 2019, 17:32:42 UTC
tools/power turbostat: Make interval calculation per thread to reduce jitter
Tip revision: d4794f2
test_string.c 
// SPDX-License-Identifier: GPL-2.0-only
#include <linux/module.h>
#include <linux/printk.h>
#include <linux/slab.h>
#include <linux/string.h>

static __init int memset16_selftest(void)
{
	unsigned i, j, k;
	u16 v, *p;

	p = kmalloc(256 * 2 * 2, GFP_KERNEL);
	if (!p)
		return -1;

	for (i = 0; i < 256; i++) {
		for (j = 0; j < 256; j++) {
			memset(p, 0xa1, 256 * 2 * sizeof(v));
			memset16(p + i, 0xb1b2, j);
			for (k = 0; k < 512; k++) {
				v = p[k];
				if (k < i) {
					if (v != 0xa1a1)
						goto fail;
				} else if (k < i + j) {
					if (v != 0xb1b2)
						goto fail;
				} else {
					if (v != 0xa1a1)
						goto fail;
				}
			}
		}
	}

fail:
	kfree(p);
	if (i < 256)
		return (i << 24) | (j << 16) | k | 0x8000;
	return 0;
}

static __init int memset32_selftest(void)
{
	unsigned i, j, k;
	u32 v, *p;

	p = kmalloc(256 * 2 * 4, GFP_KERNEL);
	if (!p)
		return -1;

	for (i = 0; i < 256; i++) {
		for (j = 0; j < 256; j++) {
			memset(p, 0xa1, 256 * 2 * sizeof(v));
			memset32(p + i, 0xb1b2b3b4, j);
			for (k = 0; k < 512; k++) {
				v = p[k];
				if (k < i) {
					if (v != 0xa1a1a1a1)
						goto fail;
				} else if (k < i + j) {
					if (v != 0xb1b2b3b4)
						goto fail;
				} else {
					if (v != 0xa1a1a1a1)
						goto fail;
				}
			}
		}
	}

fail:
	kfree(p);
	if (i < 256)
		return (i << 24) | (j << 16) | k | 0x8000;
	return 0;
}

static __init int memset64_selftest(void)
{
	unsigned i, j, k;
	u64 v, *p;

	p = kmalloc(256 * 2 * 8, GFP_KERNEL);
	if (!p)
		return -1;

	for (i = 0; i < 256; i++) {
		for (j = 0; j < 256; j++) {
			memset(p, 0xa1, 256 * 2 * sizeof(v));
			memset64(p + i, 0xb1b2b3b4b5b6b7b8ULL, j);
			for (k = 0; k < 512; k++) {
				v = p[k];
				if (k < i) {
					if (v != 0xa1a1a1a1a1a1a1a1ULL)
						goto fail;
				} else if (k < i + j) {
					if (v != 0xb1b2b3b4b5b6b7b8ULL)
						goto fail;
				} else {
					if (v != 0xa1a1a1a1a1a1a1a1ULL)
						goto fail;
				}
			}
		}
	}

fail:
	kfree(p);
	if (i < 256)
		return (i << 24) | (j << 16) | k | 0x8000;
	return 0;
}

static __init int strchr_selftest(void)
{
	const char *test_string = "abcdefghijkl";
	const char *empty_string = "";
	char *result;
	int i;

	for (i = 0; i < strlen(test_string) + 1; i++) {
		result = strchr(test_string, test_string[i]);
		if (result - test_string != i)
			return i + 'a';
	}

	result = strchr(empty_string, '\0');
	if (result != empty_string)
		return 0x101;

	result = strchr(empty_string, 'a');
	if (result)
		return 0x102;

	result = strchr(test_string, 'z');
	if (result)
		return 0x103;

	return 0;
}

static __init int strnchr_selftest(void)
{
	const char *test_string = "abcdefghijkl";
	const char *empty_string = "";
	char *result;
	int i, j;

	for (i = 0; i < strlen(test_string) + 1; i++) {
		for (j = 0; j < strlen(test_string) + 2; j++) {
			result = strnchr(test_string, j, test_string[i]);
			if (j <= i) {
				if (!result)
					continue;
				return ((i + 'a') << 8) | j;
			}
			if (result - test_string != i)
				return ((i + 'a') << 8) | j;
		}
	}

	result = strnchr(empty_string, 0, '\0');
	if (result)
		return 0x10001;

	result = strnchr(empty_string, 1, '\0');
	if (result != empty_string)
		return 0x10002;

	result = strnchr(empty_string, 1, 'a');
	if (result)
		return 0x10003;

	result = strnchr(NULL, 0, '\0');
	if (result)
		return 0x10004;

	return 0;
}

static __init int string_selftest_init(void)
{
	int test, subtest;

	test = 1;
	subtest = memset16_selftest();
	if (subtest)
		goto fail;

	test = 2;
	subtest = memset32_selftest();
	if (subtest)
		goto fail;

	test = 3;
	subtest = memset64_selftest();
	if (subtest)
		goto fail;

	test = 4;
	subtest = strchr_selftest();
	if (subtest)
		goto fail;

	test = 5;
	subtest = strnchr_selftest();
	if (subtest)
		goto fail;

	pr_info("String selftests succeeded\n");
	return 0;
fail:
	pr_crit("String selftest failure %d.%08x\n", test, subtest);
	return 0;
}

module_init(string_selftest_init);
MODULE_LICENSE("GPL v2");
back to top