arch/tile/lib/memset_32.c

   1 /*
   2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  */
  14
  15 #include <arch/chip.h>
  16
  17 #include <linux/types.h>
  18 #include <linux/string.h>
  19 #include <linux/module.h>
  20
  21 #undef memset
  22
  23 void *memset(void *s, int c, size_t n)
  24 {
  25         uint32_t *out32;
  26         int n32;
  27         uint32_t v16, v32;
  28         uint8_t *out8 = s;
  29 #if !CHIP_HAS_WH64()
  30         int ahead32;
  31 #else
  32         int to_align32;
  33 #endif
  34
  35         /* Experimentation shows that a trivial tight loop is a win up until
  36          * around a size of 20, where writing a word at a time starts to win.
  37          */
  38 #define BYTE_CUTOFF 20
  39
  40 #if BYTE_CUTOFF < 3
  41         /* This must be at least at least this big, or some code later
  42          * on doesn't work.
  43          */
  44 #error "BYTE_CUTOFF is too small"
  45 #endif
  46
  47         if (n < BYTE_CUTOFF) {
  48                 /* Strangely, this turns out to be the tightest way to
  49                  * write this loop.
  50                  */
  51                 if (n != 0) {
  52                         do {
  53                                 /* Strangely, combining these into one line
  54                                  * performs worse.
  55                                  */
  56                                 *out8 = c;
  57                                 out8++;
  58                         } while (--n != 0);
  59                 }
  60
  61                 return s;
  62         }
  63
  64 #if !CHIP_HAS_WH64()
  65         /* Use a spare issue slot to start prefetching the first cache
  66          * line early. This instruction is free as the store can be buried
  67          * in otherwise idle issue slots doing ALU ops.
  68          */
  69         __insn_prefetch(out8);
  70
  71         /* We prefetch the end so that a short memset that spans two cache
  72          * lines gets some prefetching benefit. Again we believe this is free
  73          * to issue.
  74          */
  75         __insn_prefetch(&out8[n - 1]);
  76 #endif /* !CHIP_HAS_WH64() */
  77
  78
  79         /* Align 'out8'. We know n >= 3 so this won't write past the end. */
  80         while (((uintptr_t) out8 & 3) != 0) {
  81                 *out8++ = c;
  82                 --n;
  83         }
  84
  85         /* Align 'n'. */
  86         while (n & 3)
  87                 out8[--n] = c;
  88
  89         out32 = (uint32_t *) out8;
  90         n32 = n >> 2;
  91
  92         /* Tile input byte out to 32 bits. */
  93         v16 = __insn_intlb(c, c);
  94         v32 = __insn_intlh(v16, v16);
  95
  96         /* This must be at least 8 or the following loop doesn't work. */
  97 #define CACHE_LINE_SIZE_IN_WORDS (CHIP_L2_LINE_SIZE() / 4)
  98
  99 #if !CHIP_HAS_WH64()
 100
 101         ahead32 = CACHE_LINE_SIZE_IN_WORDS;
 102
 103         /* We already prefetched the first and last cache lines, so
 104          * we only need to do more prefetching if we are storing
 105          * to more than two cache lines.
 106          */
 107         if (n32 > CACHE_LINE_SIZE_IN_WORDS * 2) {
 108                 int i;
 109
 110                 /* Prefetch the next several cache lines.
 111                  * This is the setup code for the software-pipelined
 112                  * loop below.
 113                  */
 114 #define MAX_PREFETCH 5
 115                 ahead32 = n32 & -CACHE_LINE_SIZE_IN_WORDS;
 116                 if (ahead32 > MAX_PREFETCH * CACHE_LINE_SIZE_IN_WORDS)
 117                         ahead32 = MAX_PREFETCH * CACHE_LINE_SIZE_IN_WORDS;
 118
 119                 for (i = CACHE_LINE_SIZE_IN_WORDS;
 120                      i < ahead32; i += CACHE_LINE_SIZE_IN_WORDS)
 121                         __insn_prefetch(&out32[i]);
 122         }
 123
 124         if (n32 > ahead32) {
 125                 while (1) {
 126                         int j;
 127
 128                         /* Prefetch by reading one word several cache lines
 129                          * ahead.  Since loads are non-blocking this will
 130                          * cause the full cache line to be read while we are
 131                          * finishing earlier cache lines.  Using a store
 132                          * here causes microarchitectural performance
 133                          * problems where a victimizing store miss goes to
 134                          * the head of the retry FIFO and locks the pipe for
 135                          * a few cycles.  So a few subsequent stores in this
 136                          * loop go into the retry FIFO, and then later
 137                          * stores see other stores to the same cache line
 138                          * are already in the retry FIFO and themselves go
 139                          * into the retry FIFO, filling it up and grinding
 140                          * to a halt waiting for the original miss to be
 141                          * satisfied.
 142                          */
 143                         __insn_prefetch(&out32[ahead32]);
 144
 145 #if CACHE_LINE_SIZE_IN_WORDS % 4 != 0
 146 #error "Unhandled CACHE_LINE_SIZE_IN_WORDS"
 147 #endif
 148
 149                         n32 -= CACHE_LINE_SIZE_IN_WORDS;
 150
 151                         /* Save icache space by only partially unrolling
 152                          * this loop.
 153                          */
 154                         for (j = CACHE_LINE_SIZE_IN_WORDS / 4; j > 0; j--) {
 155                                 *out32++ = v32;
 156                                 *out32++ = v32;
 157                                 *out32++ = v32;
 158                                 *out32++ = v32;
 159                         }
 160
 161                         /* To save compiled code size, reuse this loop even
 162                          * when we run out of prefetching to do by dropping
 163                          * ahead32 down.
 164                          */
 165                         if (n32 <= ahead32) {
 166                                 /* Not even a full cache line left,
 167                                  * so stop now.
 168                                  */
 169                                 if (n32 < CACHE_LINE_SIZE_IN_WORDS)
 170                                         break;
 171
 172                                 /* Choose a small enough value that we don't
 173                                  * prefetch past the end.  There's no sense
 174                                  * in touching cache lines we don't have to.
 175                                  */
 176                                 ahead32 = CACHE_LINE_SIZE_IN_WORDS - 1;
 177                         }
 178                 }
 179         }
 180
 181 #else /* CHIP_HAS_WH64() */
 182
 183         /* Determine how many words we need to emit before the 'out32'
 184          * pointer becomes aligned modulo the cache line size.
 185          */
 186         to_align32 =
 187                 (-((uintptr_t)out32 >> 2)) & (CACHE_LINE_SIZE_IN_WORDS - 1);
 188
 189         /* Only bother aligning and using wh64 if there is at least
 190          * one full cache line to process.  This check also prevents
 191          * overrunning the end of the buffer with alignment words.
 192          */
 193         if (to_align32 <= n32 - CACHE_LINE_SIZE_IN_WORDS) {
 194                 int lines_left;
 195
 196                 /* Align out32 mod the cache line size so we can use wh64. */
 197                 n32 -= to_align32;
 198                 for (; to_align32 != 0; to_align32--) {
 199                         *out32 = v32;
 200                         out32++;
 201                 }
 202
 203                 /* Use unsigned divide to turn this into a right shift. */
 204                 lines_left = (unsigned)n32 / CACHE_LINE_SIZE_IN_WORDS;
 205
 206                 do {
 207                         /* Only wh64 a few lines at a time, so we don't
 208                          * exceed the maximum number of victim lines.
 209                          */
 210                         int x = ((lines_left < CHIP_MAX_OUTSTANDING_VICTIMS())
 211                                   ? lines_left
 212                                   : CHIP_MAX_OUTSTANDING_VICTIMS());
 213                         uint32_t *wh = out32;
 214                         int i = x;
 215                         int j;
 216
 217                         lines_left -= x;
 218
 219                         do {
 220                                 __insn_wh64(wh);
 221                                 wh += CACHE_LINE_SIZE_IN_WORDS;
 222                         } while (--i);
 223
 224                         for (j = x * (CACHE_LINE_SIZE_IN_WORDS / 4);
 225                              j != 0; j--) {
 226                                 *out32++ = v32;
 227                                 *out32++ = v32;
 228                                 *out32++ = v32;
 229                                 *out32++ = v32;
 230                         }
 231                 } while (lines_left != 0);
 232
 233                 /* We processed all full lines above, so only this many
 234                  * words remain to be processed.
 235                  */
 236                 n32 &= CACHE_LINE_SIZE_IN_WORDS - 1;
 237         }
 238
 239 #endif /* CHIP_HAS_WH64() */
 240
 241         /* Now handle any leftover values. */
 242         if (n32 != 0) {
 243                 do {
 244                         *out32 = v32;
 245                         out32++;
 246                 } while (--n32 != 0);
 247         }
 248
 249         return s;
 250 }
 251 EXPORT_SYMBOL(memset);