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Commit 648eee52 authored by Robin Getz's avatar Robin Getz Committed by Mike Frysinger
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Blackfin: optimize strncpy a bit 



Add a little strncpy optimization which can easily cut boot time by 20%.

When the kernel is booting with initramfs, it builds up the filesystem
from a cpio archive by calling strncpy_from_user() via fs/namei.c's
do_getname() on every file in the archive (which can be lots) with a
length of PATH_MAX (1024).  This causes the dest of the strncpy to be
padded with many NUL bytes.

This optimization mostly causes these NUL bytes to be padded with a call
to memset() which is already optimized for filling memory quickly, but
the hardware loop helps a little bit as well.

Boot time measured with 'loglevel=0' so UART speed doesn't get in the way.

Signed-off-by: default avatarRobin Getz <robin.getz@analog.com>
Signed-off-by: default avatarMike Frysinger <vapier@gentoo.org>
parent c70dcabc

arch/blackfin/lib/memset.S

+1 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
 * R1 = filler byte

 * R2 = count

 * Favours word aligned data.

 * The strncpy assumes that I0 and I1 are not used in this function

 */



ENTRY(_memset)

arch/blackfin/lib/strncpy.S

+46 −13
Original line number Diff line number Diff line
@@ -5,12 +5,14 @@ 
 */



#include <linux/linkage.h>

#include <asm/context.S>



/* void *strncpy(char *dest, const char *src, size_t n);

 * R0 = address (dest)

 * R1 = address (src)

 * R2 = size

 * Returns a pointer to the destination string dest

 * Returns a pointer (R0) to the destination string dest

 *  we do this by not changing R0

 */



#ifdef CONFIG_STRNCPY_L1
@@ -24,29 +26,60 @@ 
ENTRY(_strncpy)

	CC = R2 == 0;

	if CC JUMP 4f;



	P2 = R2 ;       /* size */

	P0 = R0 ;       /* dst*/

	P1 = R1 ;       /* src*/



	LSETUP (1f, 2f) LC0 = P2;

1:

	R1 = B [P1++] (Z);

	B [P0++] = R1;

	CC = R1;

	if ! cc jump 2f;

	R2 += -1;

	CC = R2 == 0;

	if ! cc jump 1b (bp);

	jump 4f;

	CC = R1 == 0;

2:

	/* if src is shorter than n, we need to null pad bytes in dest */

	R1 = 0;

	if CC jump 3f;



	RTS;



	/* if src is shorter than n, we need to null pad bytes in dest

	 * but, we can get here when the last byte is zero, and we don't

	 * want to copy an extra byte at the end, so we need to check

	 */

3:

	R2 = LC0;

	CC = R2

	if ! CC jump 6f;



	/* if the required null padded portion is small, do it here, rather than

	 * handling the overhead of memset (which is OK when things are big).

	 */

	R3 = 0x20;

	CC = R2 < R3;

	IF CC jump 4f;



	R2 += -1;

	CC = R2 == 0;

	if cc jump 4f;

	B [P0++] = R1;

	jump 3b;



	/* Set things up for memset

	 * R0 = address

	 * R1 = filler byte (this case it's zero, set above)

	 * R2 = count (set above)

	 */



	I1 = R0;

	R0 = RETS;

	I0 = R0;

	R0 = P0;

	pseudo_long_call _memset, p0;

	R0 = I0;

	RETS = R0;

	R0 = I1;

	RTS;



4:

	LSETUP(5f, 5f) LC0;

5:

	B [P0++] = R1;

6:

	RTS;



ENDPROC(_strncpy)