memcpy.c

linux-2.6.15.6

/*
 *    Optimized memory copy routines.
 *
 *    Copyright (C) 2004 Randolph Chung <[e-mail]>
 *
 *    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 2, 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, write to the Free Software
 *    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 *    Portions derived from the GNU C Library
 *    Copyright (C) 1991, 1997, 2003 Free Software Foundation, Inc.
 *
 * Several strategies are tried to try to get the best performance for various
 * conditions. In the optimal case, we copy 64-bytes in an unrolled loop using 
 * fp regs. This is followed by loops that copy 32- or 16-bytes at a time using
 * general registers.  Unaligned copies are handled either by aligning the 
 * destination and then using shift-and-write method, or in a few cases by 
 * falling back to a byte-at-a-time copy.
 *
 * I chose to implement this in C because it is easier to maintain and debug,
 * and in my experiments it appears that the C code generated by gcc (3.3/3.4
 * at the time of writing) is fairly optimal. Unfortunately some of the 
 * semantics of the copy routine (exception handling) is difficult to express
 * in C, so we have to play some tricks to get it to work.
 *
 * All the loads and stores are done via explicit asm() code in order to use
 * the right space registers. 
 * 
 * Testing with various alignments and buffer sizes shows that this code is 
 * often >10x faster than a simple byte-at-a-time copy, even for strangely
 * aligned operands. It is interesting to note that the glibc version
 * of memcpy (written in C) is actually quite fast already. This routine is 
 * able to beat it by 30-40% for aligned copies because of the loop unrolling, 
 * but in some cases the glibc version is still slightly faster. This lends 
 * more credibility that gcc can generate very good code as long as we are 
 * careful.
 *
 * TODO:
 * - cache prefetching needs more experimentation to get optimal settings
 * - try not to use the post-increment address modifiers; they create additional
 *   interlocks
 * - replace byte-copy loops with stybs sequences
 */

#ifdef __KERNEL__
#include <linux/config.h>
#include <linux/module.h>
#include <linux/compiler.h>
#include <asm/uaccess.h>
#define s_space "%%sr1"
#define d_space "%%sr2"
#else
#include "memcpy.h"
#define s_space "%%sr0"
#define d_space "%%sr0"
#define pa_memcpy new2_copy
#endif

DECLARE_PER_CPU(struct exception_data, exception_data);

#define preserve_branch(label)	do {					\
	volatile int dummy;						\
	/* The following branch is never taken, it's just here to  */	\
	/* prevent gcc from optimizing away our exception code. */ 	\
	if (unlikely(dummy != dummy))					\
		goto label;						\
} while (0)

#define get_user_space() (segment_eq(get_fs(), KERNEL_DS) ? 0 : mfsp(3))
#define get_kernel_space() (0)

#define MERGE(w0, sh_1, w1, sh_2)  ({					\
	unsigned int _r;						\
	asm volatile (							\
	"mtsar %3\n"							\
	"shrpw %1, %2, %%sar, %0\n"					\
	: "=r"(_r)							\
	: "r"(w0), "r"(w1), "r"(sh_2)					\
	);								\
	_r;								\
})
#define THRESHOLD	16

#ifdef DEBUG_MEMCPY
#define DPRINTF(fmt, args...) do { printk(KERN_DEBUG "%s:%d:%s ", __FILE__, __LINE__, __FUNCTION__ ); printk(KERN_DEBUG fmt, ##args ); } while (0)
#else
#define DPRINTF(fmt, args...)
#endif

#ifndef __LP64__
#define EXC_WORD ".word"
#else
#define EXC_WORD ".dword"
#endif

#define def_load_ai_insn(_insn,_sz,_tt,_s,_a,_t,_e)	\
	__asm__ __volatile__ (				\
	"1:\t" #_insn ",ma " #_sz "(" _s ",%1), %0\n" 	\
	"\t.section __ex_table,\"aw\"\n"		\
	"\t" EXC_WORD "\t1b\n"				\
	"\t" EXC_WORD "\t" #_e "\n"			\
	"\t.previous\n"					\
	: _tt(_t), "+r"(_a)				\
	: 						\
	: "r8")

#define def_store_ai_insn(_insn,_sz,_tt,_s,_a,_t,_e) 	\
	__asm__ __volatile__ (				\
	"1:\t" #_insn ",ma %1, " #_sz "(" _s ",%0)\n" 	\
	"\t.section __ex_table,\"aw\"\n"		\
	"\t" EXC_WORD "\t1b\n"				\
	"\t" EXC_WORD "\t" #_e "\n"			\
	"\t.previous\n"					\
	: "+r"(_a) 					\
	: _tt(_t)					\
	: "r8")

#define ldbma(_s, _a, _t, _e) def_load_ai_insn(ldbs,1,"=r",_s,_a,_t,_e)
#define stbma(_s, _t, _a, _e) def_store_ai_insn(stbs,1,"r",_s,_a,_t,_e)
#define ldwma(_s, _a, _t, _e) def_load_ai_insn(ldw,4,"=r",_s,_a,_t,_e)
#define stwma(_s, _t, _a, _e) def_store_ai_insn(stw,4,"r",_s,_a,_t,_e)
#define flddma(_s, _a, _t, _e) def_load_ai_insn(fldd,8,"=f",_s,_a,_t,_e)
#define fstdma(_s, _t, _a, _e) def_store_ai_insn(fstd,8,"f",_s,_a,_t,_e)

#define def_load_insn(_insn,_tt,_s,_o,_a,_t,_e) 	\
	__asm__ __volatile__ (				\
	"1:\t" #_insn " " #_o "(" _s ",%1), %0\n"	\
	"\t.section __ex_table,\"aw\"\n"		\
	"\t" EXC_WORD "\t1b\n"				\
	"\t" EXC_WORD "\t" #_e "\n"			\
	"\t.previous\n"					\
	: _tt(_t) 					\
	: "r"(_a)					\
	: "r8")

#define def_store_insn(_insn,_tt,_s,_t,_o,_a,_e) 	\
	__asm__ __volatile__ (				\
	"1:\t" #_insn " %0, " #_o "(" _s ",%1)\n" 	\
	"\t.section __ex_table,\"aw\"\n"		\
	"\t" EXC_WORD "\t1b\n"				\
	"\t" EXC_WORD "\t" #_e "\n"			\
	"\t.previous\n"					\
	: 						\
	: _tt(_t), "r"(_a)				\
	: "r8")

#define ldw(_s,_o,_a,_t,_e)	def_load_insn(ldw,"=r",_s,_o,_a,_t,_e)
#define stw(_s,_t,_o,_a,_e) 	def_store_insn(stw,"r",_s,_t,_o,_a,_e)

#ifdef  CONFIG_PREFETCH
extern inline void prefetch_src(const void *addr)
{
	__asm__("ldw 0(" s_space ",%0), %%r0" : : "r" (addr));
}

extern inline void prefetch_dst(const void *addr)
{
	__asm__("ldd 0(" d_space ",%0), %%r0" : : "r" (addr));
}
#else
#define prefetch_src(addr)
#define prefetch_dst(addr)
#endif

/* Copy from a not-aligned src to an aligned dst, using shifts. Handles 4 words
 * per loop.  This code is derived from glibc. 
 */
static inline unsigned long copy_dstaligned(unsigned long dst, unsigned long src, unsigned long len, unsigned long o_dst, unsigned long o_src, unsigned long o_len)
{
	/* gcc complains that a2 and a3 may be uninitialized, but actually
	 * they cannot be.  Initialize a2/a3 to shut gcc up.
	 */
	register unsigned int a0, a1, a2 = 0, a3 = 0;
	int sh_1, sh_2;
	struct exception_data *d;

	/* prefetch_src((const void *)src); */

	/* Calculate how to shift a word read at the memory operation
	   aligned srcp to make it aligned for copy.  */
	sh_1 = 8 * (src % sizeof(unsigned int));
	sh_2 = 8 * sizeof(unsigned int) - sh_1;

	/* Make src aligned by rounding it down.  */
	src &= -sizeof(unsigned int);

	switch (len % 4)
	{
		case 2:
			/* a1 = ((unsigned int *) src)[0];
			   a2 = ((unsigned int *) src)[1]; */
			ldw(s_space, 0, src, a1, cda_ldw_exc);
			ldw(s_space, 4, src, a2, cda_ldw_exc);
			src -= 1 * sizeof(unsigned int);
			dst -= 3 * sizeof(unsigned int);
			len += 2;
			goto do1;
		case 3:
			/* a0 = ((unsigned int *) src)[0];
			   a1 = ((unsigned int *) src)[1]; */
			ldw(s_space, 0, src, a0, cda_ldw_exc);
			ldw(s_space, 4, src, a1, cda_ldw_exc);
			src -= 0 * sizeof(unsigned int);
			dst -= 2 * sizeof(unsigned int);
			len += 1;
			goto do2;
		case 0:
			if (len == 0)
				return 0;
			/* a3 = ((unsigned int *) src)[0];
			   a0 = ((unsigned int *) src)[1]; */
			ldw(s_space, 0, src, a3, cda_ldw_exc);
			ldw(s_space, 4, src, a0, cda_ldw_exc);
			src -=-1 * sizeof(unsigned int);
			dst -= 1 * sizeof(unsigned int);
			len += 0;
			goto do3;
		case 1:
			/* a2 = ((unsigned int *) src)[0];
			   a3 = ((unsigned int *) src)[1]; */
			ldw(s_space, 0, src, a2, cda_ldw_exc);
			ldw(s_space, 4, src, a3, cda_ldw_exc);
			src -=-2 * sizeof(unsigned int);
			dst -= 0 * sizeof(unsigned int);
			len -= 1;
			if (len == 0)
				goto do0;
			goto do4;			/* No-op.  */
	}

	do
	{
		/* prefetch_src((const void *)(src + 4 * sizeof(unsigned int))); */
do4:
		/* a0 = ((unsigned int *) src)[0]; */
		ldw(s_space, 0, src, a0, cda_ldw_exc);
		/* ((unsigned int *) dst)[0] = MERGE (a2, sh_1, a3, sh_2); */
		stw(d_space, MERGE (a2, sh_1, a3, sh_2), 0, dst, cda_stw_exc);
do3:
		/* a1 = ((unsigned int *) src)[1]; */
		ldw(s_space, 4, src, a1, cda_ldw_exc);
		/* ((unsigned int *) dst)[1] = MERGE (a3, sh_1, a0, sh_2); */
		stw(d_space, MERGE (a3, sh_1, a0, sh_2), 4, dst, cda_stw_exc);
do2:
		/* a2 = ((unsigned int *) src)[2]; */
		ldw(s_space, 8, src, a2, cda_ldw_exc);
		/* ((unsigned int *) dst)[2] = MERGE (a0, sh_1, a1, sh_2); */
		stw(d_space, MERGE (a0, sh_1, a1, sh_2), 8, dst, cda_stw_exc);
do1:
		/* a3 = ((unsigned int *) src)[3]; */
		ldw(s_space, 12, src, a3, cda_ldw_exc);
		/* ((unsigned int *) dst)[3] = MERGE (a1, sh_1, a2, sh_2); */
		stw(d_space, MERGE (a1, sh_1, a2, sh_2), 12, dst, cda_stw_exc);