/*

 * 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 */