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
memset(void * s,int c,size_t n)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);
252