/*
 * Copyright (c) 2020 Red Hat, Inc.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA. 
 *
 * $Id: //eng/uds-releases/jasper/src/uds/cpu.h#1 $
 */

#ifndef CPU_H
#define CPU_H

#include "compiler.h"
#include "typeDefs.h"

/**
 * The number of bytes in a CPU cache line. In the future, we'll probably need
 * to move this to a processor-specific file or discover it at compilation
 * time (or runtime, if sufficiently heterogeneous), but this will do for now.
 * (Must be a \#define since enums are not proper compile-time constants.)
 **/
#ifdef __PPC__
// N.B.: Some PPC processors have smaller cache lines.
#define CACHE_LINE_BYTES 128
#elif defined(__s390x__)
#define CACHE_LINE_BYTES 256
#elif defined(__x86_64__) || defined(__aarch64__)
#define CACHE_LINE_BYTES  64
#else
#error "unknown cache line size"
#endif

/**
 * Minimize cache-miss latency by moving data into a CPU cache before it is
 * accessed.
 *
 * @param address   the address to fetch (may be invalid)
 * @param forWrite  must be constant at compile time--false if
 *                  for reading, true if for writing
 **/
static INLINE void prefetchAddress(const void *address, bool forWrite)
{
  // forWrite won't won't be a constant if we are compiled with optimization
  // turned off, in which case prefetching really doesn't matter.
  if (__builtin_constant_p(forWrite)) {
    __builtin_prefetch(address, forWrite);
  }
}

/**
 * Minimize cache-miss latency by moving a range of addresses into a
 * CPU cache before they are accessed.
 *
 * @param start     the starting address to fetch (may be invalid)
 * @param size      the number of bytes in the address range
 * @param forWrite  must be constant at compile time--false if
 *                  for reading, true if for writing
 **/
static INLINE void prefetchRange(const void   *start,
                                 unsigned int  size,
                                 bool          forWrite)
{
  // Count the number of cache lines to fetch, allowing for the address range
  // to span an extra cache line boundary due to address alignment.
  const char *address = (const char *) start;
  unsigned int offset = ((uintptr_t) address % CACHE_LINE_BYTES);
  size += offset;

  unsigned int cacheLines = (1 + (size / CACHE_LINE_BYTES));
  while (cacheLines-- > 0) {
    prefetchAddress(address, forWrite);
    address += CACHE_LINE_BYTES;
  }
}

#endif /* CPU_H */