arch/tile/lib/memset_32.c - kernel/bruno - Git at Google

 /*
  * 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);
	/*
	* 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);