tools/testing/selftests/resctrl/fill_buf.c

Source file repositories/reference/linux-study-clean/tools/testing/selftests/resctrl/fill_buf.c

File Facts

System
Linux kernel
Corpus path
tools/testing/selftests/resctrl/fill_buf.c
Extension
.c
Size
3069 bytes
Lines
145
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0
/*
 * fill_buf benchmark
 *
 * Copyright (C) 2018 Intel Corporation
 *
 * Authors:
 *    Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
 *    Fenghua Yu <fenghua.yu@intel.com>
 */
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <inttypes.h>
#include <string.h>

#include "resctrl.h"

#define CL_SIZE			(64)
#define PAGE_SIZE		(4 * 1024)
#define MB			(1024 * 1024)

static void sb(void)
{
#if defined(__i386) || defined(__x86_64)
	asm volatile("sfence\n\t"
		     : : : "memory");
#endif
}

static void cl_flush(void *p)
{
#if defined(__i386) || defined(__x86_64)
	asm volatile("clflush (%0)\n\t"
		     : : "r"(p) : "memory");
#endif
}

void mem_flush(unsigned char *buf, size_t buf_size)
{
	unsigned char *cp = buf;
	size_t i = 0;

	buf_size = buf_size / CL_SIZE; /* mem size in cache lines */

	for (i = 0; i < buf_size; i++)
		cl_flush(&cp[i * CL_SIZE]);

	sb();
}

/*
 * Buffer index step advance to workaround HW prefetching interfering with
 * the measurements.
 *
 * Must be a prime to step through all indexes of the buffer.
 *
 * Some primes work better than others on some architectures (from MBA/MBM
 * result stability point of view).
 */
#define FILL_IDX_MULT	23

static int fill_one_span_read(unsigned char *buf, size_t buf_size)
{
	unsigned int size = buf_size / (CL_SIZE / 2);
	unsigned int i, idx = 0;
	unsigned char sum = 0;

	/*
	 * Read the buffer in an order that is unexpected by HW prefetching
	 * optimizations to prevent them interfering with the caching pattern.
	 *
	 * The read order is (in terms of halves of cachelines):
	 *	i * FILL_IDX_MULT % size
	 * The formula is open-coded below to avoiding modulo inside the loop
	 * as it improves MBA/MBM result stability on some architectures.
	 */
	for (i = 0; i < size; i++) {
		sum += buf[idx * (CL_SIZE / 2)];

		idx += FILL_IDX_MULT;
		while (idx >= size)
			idx -= size;
	}

	return sum;
}

Annotation

Implementation Notes