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authorArnd Bergmann <arnd@arndb.de>2021-05-08 00:07:47 +0200
committerArnd Bergmann <arnd@arndb.de>2021-05-10 17:50:04 +0200
commitbf067edf5d2f5b2948ee7197974a719aae3e526c (patch)
tree5c2f652b41034e10d3c86f4e71b65c43291bf2e1 /arch/openrisc
parent637be9183e0475c430fc77162c222bcaab887989 (diff)
openrisc: always use unaligned-struct header
openrisc is the only architecture using the linux/unaligned/*memmove infrastructure. There is a comment saying that this version is more efficient, but this was added in 2011 before the openrisc gcc port was merged upstream. I checked a couple of files to see what the actual difference is with the mainline gcc (9.4 and 11.1), and found that the generic header seems to produce better code now, regardless of the gcc version. Specifically, the be_memmove leads to allocating a stack slot and copying the data one byte at a time, then reading the whole word from the stack: 00000000 <test_get_unaligned_memmove>: 0: 9c 21 ff f4 l.addi r1,r1,-12 4: d4 01 10 04 l.sw 4(r1),r2 8: 8e 63 00 00 l.lbz r19,0(r3) c: 9c 41 00 0c l.addi r2,r1,12 10: 8e 23 00 01 l.lbz r17,1(r3) 14: db e2 9f f4 l.sb -12(r2),r19 18: db e2 8f f5 l.sb -11(r2),r17 1c: 8e 63 00 02 l.lbz r19,2(r3) 20: 8e 23 00 03 l.lbz r17,3(r3) 24: d4 01 48 08 l.sw 8(r1),r9 28: db e2 9f f6 l.sb -10(r2),r19 2c: db e2 8f f7 l.sb -9(r2),r17 30: 85 62 ff f4 l.lwz r11,-12(r2) 34: 85 21 00 08 l.lwz r9,8(r1) 38: 84 41 00 04 l.lwz r2,4(r1) 3c: 44 00 48 00 l.jr r9 40: 9c 21 00 0c l.addi r1,r1,12 while the be_struct version reads each byte into a register and does a shift to the right position: 00000000 <test_get_unaligned_struct>: 0: 9c 21 ff f8 l.addi r1,r1,-8 4: 8e 63 00 00 l.lbz r19,0(r3) 8: aa 20 00 18 l.ori r17,r0,0x18 c: e2 73 88 08 l.sll r19,r19,r17 10: 8d 63 00 01 l.lbz r11,1(r3) 14: aa 20 00 10 l.ori r17,r0,0x10 18: e1 6b 88 08 l.sll r11,r11,r17 1c: e1 6b 98 04 l.or r11,r11,r19 20: 8e 23 00 02 l.lbz r17,2(r3) 24: aa 60 00 08 l.ori r19,r0,0x8 28: e2 31 98 08 l.sll r17,r17,r19 2c: d4 01 10 00 l.sw 0(r1),r2 30: d4 01 48 04 l.sw 4(r1),r9 34: 9c 41 00 08 l.addi r2,r1,8 38: e2 31 58 04 l.or r17,r17,r11 3c: 8d 63 00 03 l.lbz r11,3(r3) 40: e1 6b 88 04 l.or r11,r11,r17 44: 84 41 00 00 l.lwz r2,0(r1) 48: 85 21 00 04 l.lwz r9,4(r1) 4c: 44 00 48 00 l.jr r9 50: 9c 21 00 08 l.addi r1,r1,8 According to Stafford Horne, the new version should in fact perform better. In the trivial example, the struct version is a few instructions longer, but building a whole kernel shows an overall reduction in code size, presumably because it now has to manage fewer stack slots: text data bss dec hex filename 4792010 181480 82324 5055814 4d2546 vmlinux-unaligned-memmove 4790642 181480 82324 5054446 4d1fee vmlinux-unaligned-struct Remove the memmove version completely and let openrisc use the same code as everyone else, as a simplification. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Stafford Horne <shorne@gmail.com>
Diffstat (limited to 'arch/openrisc')
-rw-r--r--arch/openrisc/include/asm/unaligned.h47
1 files changed, 0 insertions, 47 deletions
diff --git a/arch/openrisc/include/asm/unaligned.h b/arch/openrisc/include/asm/unaligned.h
deleted file mode 100644
index 14353f2101f2..000000000000
--- a/arch/openrisc/include/asm/unaligned.h
+++ /dev/null
@@ -1,47 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-or-later */
-/*
- * OpenRISC Linux
- *
- * Linux architectural port borrowing liberally from similar works of
- * others. All original copyrights apply as per the original source
- * declaration.
- *
- * OpenRISC implementation:
- * Copyright (C) 2003 Matjaz Breskvar <phoenix@bsemi.com>
- * Copyright (C) 2010-2011 Jonas Bonn <jonas@southpole.se>
- * et al.
- */
-
-#ifndef __ASM_OPENRISC_UNALIGNED_H
-#define __ASM_OPENRISC_UNALIGNED_H
-
-/*
- * This is copied from the generic implementation and the C-struct
- * variant replaced with the memmove variant. The GCC compiler
- * for the OR32 arch optimizes too aggressively for the C-struct
- * variant to work, so use the memmove variant instead.
- *
- * It may be worth considering implementing the unaligned access
- * exception handler and allowing unaligned accesses (access_ok.h)...
- * not sure if it would be much of a performance win without further
- * investigation.
- */
-#include <asm/byteorder.h>
-
-#if defined(__LITTLE_ENDIAN)
-# include <linux/unaligned/le_memmove.h>
-# include <linux/unaligned/be_byteshift.h>
-# include <linux/unaligned/generic.h>
-# define get_unaligned __get_unaligned_le
-# define put_unaligned __put_unaligned_le
-#elif defined(__BIG_ENDIAN)
-# include <linux/unaligned/be_memmove.h>
-# include <linux/unaligned/le_byteshift.h>
-# include <linux/unaligned/generic.h>
-# define get_unaligned __get_unaligned_be
-# define put_unaligned __put_unaligned_be
-#else
-# error need to define endianess
-#endif
-
-#endif /* __ASM_OPENRISC_UNALIGNED_H */

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