- 根目录:
- arch
- tile
- lib
- memset_32.c
/*
* Copyright 2010 Tilera Corporation. All Rights Reserved.
*
* 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, version 2.
*
* 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, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for
* more details.
*/
#include <arch/chip.h>
#include <linux/types.h>
#include <linux/string.h>
#include <linux/module.h>
#undef memset
void *memset(void *s, int c, size_t n)
{
uint32_t *out32;
int n32;
uint32_t v16, v32;
uint8_t *out8 = s;
#if !CHIP_HAS_WH64()
int ahead32;
#else
int to_align32;
#endif
/* Experimentation shows that a trivial tight loop is a win up until
* around a size of 20, where writing a word at a time starts to win.
*/
#define BYTE_CUTOFF 20
#if BYTE_CUTOFF < 3
/* This must be at least at least this big, or some code later
* on doesn't work.
*/
#error "BYTE_CUTOFF is too small"
#endif
if (n < BYTE_CUTOFF) {
/* Strangely, this turns out to be the tightest way to
* write this loop.
*/
if (n != 0) {
do {
/* Strangely, combining these into one line
* performs worse.
*/
*out8 = c;
out8++;
} while (--n != 0);
}
return s;
}
#if !CHIP_HAS_WH64()
/* Use a spare issue slot to start prefetching the first cache
* line early. This instruction is free as the store can be buried
* in otherwise idle issue slots doing ALU ops.
*/
__insn_prefetch(out8);
/* We prefetch the end so that a short memset that spans two cache
* lines gets some prefetching benefit. Again we believe this is free
* to issue.
*/
__insn_prefetch(&out8[n - 1]);
#endif /* !CHIP_HAS_WH64() */
/* Align 'out8'. We know n >= 3 so this won't write past the end. */
while (((uintptr_t) out8 & 3) != 0) {
*out8++ = c;
--n;
}
/* Align 'n'. */
while (n & 3)
out8[--n] = c;
out32 = (uint32_t *) out8;
n32 = n >> 2;
/* Tile input byte out to 32 bits. */
v16 = __insn_intlb(c, c);
v32 = __insn_intlh(v16, v16);
/* This must be at least 8 or the following loop doesn't work. */
#define CACHE_LINE_SIZE_IN_WORDS (CHIP_L2_LINE_SIZE() / 4)
#if !CHIP_HAS_WH64()
ahead32 = CACHE_LINE_SIZE_IN_WORDS;
/* We already prefetched the first and last cache lines, so
* we only need to do more prefetching if we are storing
* to more than two cache lines.
*/
if (n32 > CACHE_LINE_SIZE_IN_WORDS * 2) {
int i;
/* Prefetch the next several cache lines.
* This is the setup code for the software-pipelined
* loop below.
*/
#define MAX_PREFETCH 5
ahead32 = n32 & -CACHE_LINE_SIZE_IN_WORDS;
if (ahead32 > MAX_PREFETCH * CACHE_LINE_SIZE_IN_WORDS)
ahead32 = MAX_PREFETCH * CACHE_LINE_SIZE_IN_WORDS;
for (i = CACHE_LINE_SIZE_IN_WORDS;
i < ahead32; i += CACHE_LINE_SIZE_IN_WORDS)
__insn_prefetch(&out32[i]);
}
if (n32 > ahead32) {
while (1) {
int j;
/* Prefetch by reading one word several cache lines
* ahead. Since loads are non-blocking this will
* cause the full cache line to be read while we are
* finishing earlier cache lines. Using a store
* here causes microarchitectural performance
* problems where a victimizing store miss goes to
* the head of the retry FIFO and locks the pipe for
* a few cycles. So a few subsequent stores in this
* loop go into the retry FIFO, and then later
* stores see other stores to the same cache line
* are already in the retry FIFO and themselves go
* into the retry FIFO, filling it up and grinding
* to a halt waiting for the original miss to be
* satisfied.
*/
__insn_prefetch(&out32[ahead32]);
#if CACHE_LINE_SIZE_IN_WORDS % 4 != 0
#error "Unhandled CACHE_LINE_SIZE_IN_WORDS"
#endif
n32 -= CACHE_LINE_SIZE_IN_WORDS;
/* Save icache space by only partially unrolling
* this loop.
*/
for (j = CACHE_LINE_SIZE_IN_WORDS / 4; j > 0; j--) {
*out32++ = v32;
*out32++ = v32;
*out32++ = v32;
*out32++ = v32;
}
/* To save compiled code size, reuse this loop even
* when we run out of prefetching to do by dropping
* ahead32 down.
*/
if (n32 <= ahead32) {
/* Not even a full cache line left,
* so stop now.
*/
if (n32 < CACHE_LINE_SIZE_IN_WORDS)
break;
/* Choose a small enough value that we don't
* prefetch past the end. There's no sense
* in touching cache lines we don't have to.
*/
ahead32 = CACHE_LINE_SIZE_IN_WORDS - 1;
}
}
}
#else /* CHIP_HAS_WH64() */
/* Determine how many words we need to emit before the 'out32'
* pointer becomes aligned modulo the cache line size.
*/
to_align32 =
(-((uintptr_t)out32 >> 2)) & (CACHE_LINE_SIZE_IN_WORDS - 1);
/* Only bother aligning and using wh64 if there is at least
* one full cache line to process. This check also prevents
* overrunning the end of the buffer with alignment words.
*/
if (to_align32 <= n32 - CACHE_LINE_SIZE_IN_WORDS) {
int lines_left;
/* Align out32 mod the cache line size so we can use wh64. */
n32 -= to_align32;
for (; to_align32 != 0; to_align32--) {
*out32 = v32;
out32++;
}
/* Use unsigned divide to turn this into a right shift. */
lines_left = (unsigned)n32 / CACHE_LINE_SIZE_IN_WORDS;
do {
/* Only wh64 a few lines at a time, so we don't
* exceed the maximum number of victim lines.
*/
int x = ((lines_left < CHIP_MAX_OUTSTANDING_VICTIMS())
? lines_left
: CHIP_MAX_OUTSTANDING_VICTIMS());
uint32_t *wh = out32;
int i = x;
int j;
lines_left -= x;
do {
__insn_wh64(wh);
wh += CACHE_LINE_SIZE_IN_WORDS;
} while (--i);
for (j = x * (CACHE_LINE_SIZE_IN_WORDS / 4);
j != 0; j--) {
*out32++ = v32;
*out32++ = v32;
*out32++ = v32;
*out32++ = v32;
}
} while (lines_left != 0);
/* We processed all full lines above, so only this many
* words remain to be processed.
*/
n32 &= CACHE_LINE_SIZE_IN_WORDS - 1;
}
#endif /* CHIP_HAS_WH64() */
/* Now handle any leftover values. */
if (n32 != 0) {
do {
*out32 = v32;
out32++;
} while (--n32 != 0);
}
return s;
}
EXPORT_SYMBOL(memset);