Subversion Repositories openrisc_2011-10-31

/* branch-predict.c -- branch prediction simulation

   Copyright (C) 1999 Damjan Lampret, lampret@opencores.org

   Copyright (C) 2008 Embecosm Limited

   Contributor Jeremy Bennett <jeremy.bennett@embecosm.com>

   This file is part of Or1ksim, the OpenRISC 1000 Architectural Simulator.

   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 3 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, see <http://www.gnu.org/licenses/>.  */

/* This program is commented throughout in a fashion suitable for processing

   with Doxygen. */

/* Branch prediction functions.  At the moment this functions only simulate

   functionality of branch prediction and do not influence on

   fetche/decode/execute stages.  They are here only to verify performance of

   various branch prediction configurations. */

/* Autoconf and/or portability configuration */

#include "config.h"

#include "port.h"

/* System includes */

#include <stdio.h>

#include <errno.h>

#include <stdarg.h>

/* Package includes */

#include "sim-config.h"

#include "arch.h"

#include "stats.h"

/* Branch prediction buffer */

/* Length of BPB */

#define BPB_LEN 64

/* Number of BPB ways (1, 2, 3 etc.). */

#define BPB_WAYS 1

/* Number of prediction states (2, 4, 8 etc.). */

#define BPB_PSTATES 2

/* Number of usage states (2, 3, 4 etc.). */

#define BPB_USTATES 2

/* branch prediction buffer entry */

struct bpb_entry

{

  struct

  {

    oraddr_t addr;              /* address of a branch insn */

    int taken;                  /* taken == 1, not taken == 0  OR */

    /* strongly taken == 3, taken == 2,

       not taken == 1, strongly not taken == 0 */

    int lru;                    /* least recently == 0 */

  } way[BPB_WAYS];

} bpb[BPB_LEN];

void

bpb_info ()

{

  if (!config.bpb.enabled)

    {

      PRINTF ("BPB not simulated. Check -bpb option.\n");

      return;

    }

  PRINTF ("BPB %d bytes: ",

          BPB_LEN * BPB_WAYS * (BPB_PSTATES + BPB_USTATES) / 8);

  PRINTF ("%d ways, %d sets, %d bits/prediction\n", BPB_WAYS, BPB_LEN,

          BPB_PSTATES + BPB_USTATES);

}

/* First check if branch is already in the cache and if it is:

    - increment BPB hit stats,

    - set 'lru' at this way to BPB_USTATES - 1 and

      decrement 'lru' of other ways unless they have reached 0,

    - increment correct/incorrect stats according to BPB 'taken' field

      and 'taken' variable,

    - increment or decrement BPB taken field according to 'taken' variable

   and if not:

    - increment BPB miss stats

    - find lru way and entry and replace old address with 'addr' and

      'taken' field with (BPB_PSTATES/2 - 1) + 'taken'

    - set 'lru' with BPB_USTATES - 1 and decrement 'lru' of other

      ways unless they have reached 0

*/

void

bpb_update (oraddr_t addr, int taken)

{

  int entry, way = -1;

  int i;

  /* BPB simulation enabled/disabled. */

  if (!config.bpb.enabled)

    return;

  /* Calc entry. */

  entry = addr % BPB_LEN;

  /* Scan all ways and try to find our addr. */

  for (i = 0; i < BPB_WAYS; i++)

    if (bpb[entry].way[i].addr == addr)

      way = i;

  /* Did we find our cached branch? */

  if (way >= 0)

    {                           /* Yes, we did. */

      or1k_mstats.bpb.hit++;

      for (i = 0; i < BPB_WAYS; i++)

        if (bpb[entry].way[i].lru)

          bpb[entry].way[i].lru--;

      bpb[entry].way[way].lru = BPB_USTATES - 1;

      if (bpb[entry].way[way].taken / (BPB_PSTATES / 2) == taken)

        or1k_mstats.bpb.correct++;

      else

        or1k_mstats.bpb.incorrect++;

      if (taken && (bpb[entry].way[way].taken < BPB_PSTATES - 1))

        bpb[entry].way[way].taken++;

      else if (!taken && (bpb[entry].way[way].taken))

        bpb[entry].way[way].taken--;

    }

  else

    {                           /* No, we didn't. */

      int minlru = BPB_USTATES - 1;

      int minway = 0;

      or1k_mstats.bpb.miss++;

      for (i = 0; i < BPB_WAYS; i++)

        if (bpb[entry].way[i].lru < minlru)

          minway = i;

      bpb[entry].way[minway].addr = addr;

      bpb[entry].way[minway].taken = (BPB_PSTATES / 2 - 1) + taken;

      for (i = 0; i < BPB_WAYS; i++)

        if (bpb[entry].way[i].lru)

          bpb[entry].way[i].lru--;

      bpb[entry].way[minway].lru = BPB_USTATES - 1;

    }

}

/* Branch target instruction cache */

/* Length of BTIC */

#define BTIC_LEN 128

/* Number of BTIC ways (1, 2, 3 etc.). */

#define BTIC_WAYS 2

/* Number of usage states (2, 3, 4 etc.). */

#define BTIC_USTATES 2

/* Target block size in bytes. */

#define BTIC_BLOCKSIZE 4

struct btic_entry

{

  struct

  {

    oraddr_t addr;              /* cached target address of a branch */

    int lru;                    /* least recently used */

    char *insn;                 /* cached insn at target address (not used currently) */

  } way[BTIC_WAYS];

} btic[BTIC_LEN];

void

btic_info ()

{

  if (!config.bpb.btic)

    {

      PRINTF ("BTIC not simulated. Check --btic option.\n");

      return;

    }

  PRINTF ("BTIC %d bytes: ",

          BTIC_LEN * BTIC_WAYS * (BTIC_USTATES + BTIC_BLOCKSIZE * 8) / 8);

  PRINTF ("%d ways, %d sets, %d bits/target\n", BTIC_WAYS, BTIC_LEN,

          BTIC_USTATES + BTIC_BLOCKSIZE * 8);

}

/* First check if target addr is already in the cache and if it is:

    - increment BTIC hit stats,

    - set 'lru' at this way to BTIC_USTATES - 1 and

      decrement 'lru' of other ways unless they have reached 0,

   and if not:

    - increment BTIC miss stats

    - find lru way and entry and replace old address with 'addr' and

      'insn' with NULL

    - set 'lru' with BTIC_USTATES - 1 and decrement 'lru' of other

      ways unless they have reached 0

*/

void

btic_update (oraddr_t targetaddr)

{

  int entry, way = -1;

  int i;

  /* BTIC simulation enabled/disabled. */

  if (!config.bpb.btic)

    return;

  /* Calc entry. */

  entry = targetaddr % BTIC_LEN;

  /* Scan all ways and try to find our addr. */

  for (i = 0; i < BTIC_WAYS; i++)

    if (btic[entry].way[i].addr == targetaddr)

      way = i;

  /* Did we find our cached branch? */

  if (way >= 0)

    {                           /* Yes, we did. */

      or1k_mstats.btic.hit++;

      for (i = 0; i < BTIC_WAYS; i++)

        if (btic[entry].way[i].lru)

          btic[entry].way[i].lru--;

      btic[entry].way[way].lru = BTIC_USTATES - 1;

    }

  else

    {                           /* No, we didn't. */

      int minlru = BTIC_USTATES - 1;

      int minway = 0;

      or1k_mstats.btic.miss++;

      for (i = 0; i < BTIC_WAYS; i++)

        if (btic[entry].way[i].lru < minlru)

          minway = i;

      btic[entry].way[minway].addr = targetaddr;

      btic[entry].way[minway].insn = NULL;

      for (i = 0; i < BTIC_WAYS; i++)

        if (btic[entry].way[i].lru)

          btic[entry].way[i].lru--;

      btic[entry].way[minway].lru = BTIC_USTATES - 1;

    }

}

/*----------------------------------------------------[ BPB configuration ]---*/

static void

bpb_enabled (union param_val val, void *dat)

{

  config.bpb.enabled = val.int_val;

}

static void

bpb_btic (union param_val val, void *dat)

{

  config.bpb.btic = val.int_val;

}

static void

bpb_sbp_bnf_fwd (union param_val val, void *dat)

{

  config.bpb.sbp_bnf_fwd = val.int_val;

}

static void

bpb_sbp_bf_fwd (union param_val val, void *dat)

{

  config.bpb.sbp_bf_fwd = val.int_val;

}

static void

bpb_missdelay (union param_val val, void *dat)

{

  config.bpb.missdelay = val.int_val;

}

static void

bpb_hitdelay (union param_val val, void *dat)

{

  config.bpb.hitdelay = val.int_val;

}

void

reg_bpb_sec ()

{

  struct config_section *sec = reg_config_sec ("bpb", NULL, NULL);

  reg_config_param (sec, "enabled", paramt_int, bpb_enabled);

  reg_config_param (sec, "btic", paramt_int, bpb_btic);

  reg_config_param (sec, "sbp_bnf_fwd", paramt_int, bpb_sbp_bnf_fwd);

  reg_config_param (sec, "sbp_bf_fwd", paramt_int, bpb_sbp_bf_fwd);

  reg_config_param (sec, "missdelay", paramt_int, bpb_missdelay);

  reg_config_param (sec, "hitdelay", paramt_int, bpb_hitdelay);

}