microsoft
/
WSL2-Linux-Kernel
зеркало из https://github.com/microsoft/WSL2-Linux-Kernel.git
1
0
Форкнуть 0
Код Задачи Пакеты Проекты Релизы Вики Активность
WSL2-Linux-Kernel/arch/arm/lib/memmove.S

200 строки
4.0 KiB
ArmAsm
Исходник Обычный вид История

[ARM] 2947/1: copy template with new memcpy/memmove Patch from Nicolas Pitre This patch provides a new implementation for optimized memory copy functions on ARM. It is made of two levels: a template that consists of the core copy code and separate files that define macros to be used with the core code depending on the type of copy needed. This allows for best performances while sharing the same core for implementing memcpy(), copy_from_user() and copy_to_user() for instance. Two reasons for this work: 1) the current copy_to_user/copy_from_user implementation assumes no task switch will ever occur in the middle of each copied page making it completely unsafe with CONFIG_PREEMPT=y. 2) current copy implementations are measurably suboptimal and optimizing different implementations separately is a pain and more opportunities for bugs. The reason for (1) is the fact that copy inside user pages are performed with the ldm instruction which has no mean for testing user protections and could possibly race with process preemption bypassing the COW mechanism for example. This is a longstanding issue that we said ought to be fixed for about two years now. The solution is to substitute those ldm insns with a series of ldrt or strt insns to enforce user memory protection. At least on StrongARM and XScale cores the ldm is not faster than the equivalent ldr/str insns with a warm i-cache so there is no measurable performance degradation with that change. The fact that the copy code is a template makes it pretty easy to reuse the same core code as for memcpy and benefit from the same performance optimizations. Now (2) is best demonstrated with actual throughput measurements. First, here is a summary of memcopy tests performed on a StrongARM core: PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 59.73 107.43 unaligned 32 61.31 74.72 aligned 100 132.47 136.15 unaligned 100 103.84 123.76 aligned 4096 130.67 130.80 unaligned 4096 130.68 130.64 aligned 1048576 68.03 68.18 unaligned 1048576 68.03 68.18 The buffer size is in bytes and the measured speed in MB/s. The copy was performed repeatedly with given buffer and throughput averaged over 3 seconds. Here we can see that the current kernel version has a higher entry cost that shows up with small buffers. As buffer size grows both implementation converge to the same throughput. Now here's the exact same test performed on an XScale core (PXA255): PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 46.99 77.58 unaligned 32 53.61 59.59 aligned 100 107.19 136.59 unaligned 100 83.61 97.58 aligned 4096 129.13 129.98 unaligned 4096 128.36 128.53 aligned 1048576 53.76 59.41 unaligned 1048576 33.67 56.96 Again we can see the entry setup cost being higher for the current kernel before getting to the main copy loop. Then throughput results converge as long as the buffer remains in the cache. Then the 1MB case shows more differences probably due to better pld placement and/or less instruction interlocks in this proposed implementation. Disclaimer: The PXA system was running with slower clocks than the StrongARM system so trying to infer any conclusion by comparing those separate sets of results side by side would be completely inappropriate. So... What this patch does is to replace both memcpy and memmove with an implementation based on the provided copy code template. The memmove code is kept separate since it is used only if the memory areas involved do overlap in which case the code is a transposition of the template but with the copy occurring in the opposite direction (trying to fit that mode into the template turned it into a mess not worth it for memmove alone). And obviously both memcpy and memmove were tested with all kinds of pointer alignments and buffer sizes to exercise all code paths for correctness. The next patch will provide the now trivial replacement implementation copy_to_user and copy_from_user. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2005-11-01 22:52:23 +03:00
/*
* linux/arch/arm/lib/memmove.S
*
* Author: Nicolas Pitre
* Created: Sep 28, 2005
* Copyright: (C) MontaVista Software Inc.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/linkage.h>
#include <asm/assembler.h>
.text
/*
* Prototype: void *memmove(void *dest, const void *src, size_t n);
*
* Note:
*
* If the memory regions don't overlap, we simply branch to memcpy which is
* normally a bit faster. Otherwise the copy is done going downwards. This
* is a transposition of the code from copy_template.S but with the copy
* occurring in the opposite direction.
*/
ENTRY(memmove)
subs ip, r0, r1
cmphi r2, ip
bls memcpy
stmfd sp!, {r0, r4, lr}
add r1, r1, r2
add r0, r0, r2
subs r2, r2, #4
blt 8f
ands ip, r0, #3
PLD( pld [r1, #-4] )
bne 9f
ands ip, r1, #3
bne 10f
1: subs r2, r2, #(28)
stmfd sp!, {r5 - r8}
blt 5f
[ARM] cache align destination pointer when copying memory for some processors The implementation for memory copy functions on ARM had a (disabled) provision for aligning the source pointer before loading registers with data. Turns out that aligning the _destination_ pointer is much more useful, as the read side is already sufficiently helped with the use of preload. So this changes the definition of the CALGN() macro to target the destination pointer instead, and turns it on for Feroceon processors where the gain is very noticeable. Signed-off-by: Nicolas Pitre <nico@marvell.com> Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
2008-03-31 20:38:31 +04:00
CALGN( ands ip, r0, #31 )
[ARM] 2947/1: copy template with new memcpy/memmove Patch from Nicolas Pitre This patch provides a new implementation for optimized memory copy functions on ARM. It is made of two levels: a template that consists of the core copy code and separate files that define macros to be used with the core code depending on the type of copy needed. This allows for best performances while sharing the same core for implementing memcpy(), copy_from_user() and copy_to_user() for instance. Two reasons for this work: 1) the current copy_to_user/copy_from_user implementation assumes no task switch will ever occur in the middle of each copied page making it completely unsafe with CONFIG_PREEMPT=y. 2) current copy implementations are measurably suboptimal and optimizing different implementations separately is a pain and more opportunities for bugs. The reason for (1) is the fact that copy inside user pages are performed with the ldm instruction which has no mean for testing user protections and could possibly race with process preemption bypassing the COW mechanism for example. This is a longstanding issue that we said ought to be fixed for about two years now. The solution is to substitute those ldm insns with a series of ldrt or strt insns to enforce user memory protection. At least on StrongARM and XScale cores the ldm is not faster than the equivalent ldr/str insns with a warm i-cache so there is no measurable performance degradation with that change. The fact that the copy code is a template makes it pretty easy to reuse the same core code as for memcpy and benefit from the same performance optimizations. Now (2) is best demonstrated with actual throughput measurements. First, here is a summary of memcopy tests performed on a StrongARM core: PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 59.73 107.43 unaligned 32 61.31 74.72 aligned 100 132.47 136.15 unaligned 100 103.84 123.76 aligned 4096 130.67 130.80 unaligned 4096 130.68 130.64 aligned 1048576 68.03 68.18 unaligned 1048576 68.03 68.18 The buffer size is in bytes and the measured speed in MB/s. The copy was performed repeatedly with given buffer and throughput averaged over 3 seconds. Here we can see that the current kernel version has a higher entry cost that shows up with small buffers. As buffer size grows both implementation converge to the same throughput. Now here's the exact same test performed on an XScale core (PXA255): PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 46.99 77.58 unaligned 32 53.61 59.59 aligned 100 107.19 136.59 unaligned 100 83.61 97.58 aligned 4096 129.13 129.98 unaligned 4096 128.36 128.53 aligned 1048576 53.76 59.41 unaligned 1048576 33.67 56.96 Again we can see the entry setup cost being higher for the current kernel before getting to the main copy loop. Then throughput results converge as long as the buffer remains in the cache. Then the 1MB case shows more differences probably due to better pld placement and/or less instruction interlocks in this proposed implementation. Disclaimer: The PXA system was running with slower clocks than the StrongARM system so trying to infer any conclusion by comparing those separate sets of results side by side would be completely inappropriate. So... What this patch does is to replace both memcpy and memmove with an implementation based on the provided copy code template. The memmove code is kept separate since it is used only if the memory areas involved do overlap in which case the code is a transposition of the template but with the copy occurring in the opposite direction (trying to fit that mode into the template turned it into a mess not worth it for memmove alone). And obviously both memcpy and memmove were tested with all kinds of pointer alignments and buffer sizes to exercise all code paths for correctness. The next patch will provide the now trivial replacement implementation copy_to_user and copy_from_user. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2005-11-01 22:52:23 +03:00
CALGN( sbcnes r4, ip, r2 ) @ C is always set here
CALGN( bcs 2f )
CALGN( adr r4, 6f )
CALGN( subs r2, r2, ip ) @ C is set here
[ARM] fix cache alignment code in memset.S This code is currently disabled, which explains why no one was affected. Signed-off-by: Nicolas Pitre <nico@marvell.com> Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
2008-06-11 20:40:13 +04:00
CALGN( rsb ip, ip, #32 )
[ARM] 2947/1: copy template with new memcpy/memmove Patch from Nicolas Pitre This patch provides a new implementation for optimized memory copy functions on ARM. It is made of two levels: a template that consists of the core copy code and separate files that define macros to be used with the core code depending on the type of copy needed. This allows for best performances while sharing the same core for implementing memcpy(), copy_from_user() and copy_to_user() for instance. Two reasons for this work: 1) the current copy_to_user/copy_from_user implementation assumes no task switch will ever occur in the middle of each copied page making it completely unsafe with CONFIG_PREEMPT=y. 2) current copy implementations are measurably suboptimal and optimizing different implementations separately is a pain and more opportunities for bugs. The reason for (1) is the fact that copy inside user pages are performed with the ldm instruction which has no mean for testing user protections and could possibly race with process preemption bypassing the COW mechanism for example. This is a longstanding issue that we said ought to be fixed for about two years now. The solution is to substitute those ldm insns with a series of ldrt or strt insns to enforce user memory protection. At least on StrongARM and XScale cores the ldm is not faster than the equivalent ldr/str insns with a warm i-cache so there is no measurable performance degradation with that change. The fact that the copy code is a template makes it pretty easy to reuse the same core code as for memcpy and benefit from the same performance optimizations. Now (2) is best demonstrated with actual throughput measurements. First, here is a summary of memcopy tests performed on a StrongARM core: PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 59.73 107.43 unaligned 32 61.31 74.72 aligned 100 132.47 136.15 unaligned 100 103.84 123.76 aligned 4096 130.67 130.80 unaligned 4096 130.68 130.64 aligned 1048576 68.03 68.18 unaligned 1048576 68.03 68.18 The buffer size is in bytes and the measured speed in MB/s. The copy was performed repeatedly with given buffer and throughput averaged over 3 seconds. Here we can see that the current kernel version has a higher entry cost that shows up with small buffers. As buffer size grows both implementation converge to the same throughput. Now here's the exact same test performed on an XScale core (PXA255): PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 46.99 77.58 unaligned 32 53.61 59.59 aligned 100 107.19 136.59 unaligned 100 83.61 97.58 aligned 4096 129.13 129.98 unaligned 4096 128.36 128.53 aligned 1048576 53.76 59.41 unaligned 1048576 33.67 56.96 Again we can see the entry setup cost being higher for the current kernel before getting to the main copy loop. Then throughput results converge as long as the buffer remains in the cache. Then the 1MB case shows more differences probably due to better pld placement and/or less instruction interlocks in this proposed implementation. Disclaimer: The PXA system was running with slower clocks than the StrongARM system so trying to infer any conclusion by comparing those separate sets of results side by side would be completely inappropriate. So... What this patch does is to replace both memcpy and memmove with an implementation based on the provided copy code template. The memmove code is kept separate since it is used only if the memory areas involved do overlap in which case the code is a transposition of the template but with the copy occurring in the opposite direction (trying to fit that mode into the template turned it into a mess not worth it for memmove alone). And obviously both memcpy and memmove were tested with all kinds of pointer alignments and buffer sizes to exercise all code paths for correctness. The next patch will provide the now trivial replacement implementation copy_to_user and copy_from_user. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2005-11-01 22:52:23 +03:00
CALGN( add pc, r4, ip )
PLD( pld [r1, #-4] )
2: PLD( subs r2, r2, #96 )
PLD( pld [r1, #-32] )
PLD( blt 4f )
PLD( pld [r1, #-64] )
PLD( pld [r1, #-96] )
3: PLD( pld [r1, #-128] )
4: ldmdb r1!, {r3, r4, r5, r6, r7, r8, ip, lr}
subs r2, r2, #32
stmdb r0!, {r3, r4, r5, r6, r7, r8, ip, lr}
bge 3b
PLD( cmn r2, #96 )
PLD( bge 4b )
5: ands ip, r2, #28
rsb ip, ip, #32
addne pc, pc, ip @ C is always clear here
b 7f
ARM: 6006/1: ARM: Use the correct NOP size in memmove for Thumb-2 kernel builds When compiling the kernel to Thumb-2, using a 16-bit NOP in the memmove() implementation causes the preceding ADD PC instruction to branch incorrectly in the middle of a 32-bit LDR or STR instruction. The memmove() code is now similar to the memcpy() template. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-03-29 13:29:46 +04:00
6: W(nop)
Thumb-2: Implement the unified arch/arm/lib functions This patch adds the ARM/Thumb-2 unified support for the arch/arm/lib/* files. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2009-07-24 15:32:57 +04:00
W(ldr) r3, [r1, #-4]!
W(ldr) r4, [r1, #-4]!
W(ldr) r5, [r1, #-4]!
W(ldr) r6, [r1, #-4]!
W(ldr) r7, [r1, #-4]!
W(ldr) r8, [r1, #-4]!
W(ldr) lr, [r1, #-4]!
[ARM] 2947/1: copy template with new memcpy/memmove Patch from Nicolas Pitre This patch provides a new implementation for optimized memory copy functions on ARM. It is made of two levels: a template that consists of the core copy code and separate files that define macros to be used with the core code depending on the type of copy needed. This allows for best performances while sharing the same core for implementing memcpy(), copy_from_user() and copy_to_user() for instance. Two reasons for this work: 1) the current copy_to_user/copy_from_user implementation assumes no task switch will ever occur in the middle of each copied page making it completely unsafe with CONFIG_PREEMPT=y. 2) current copy implementations are measurably suboptimal and optimizing different implementations separately is a pain and more opportunities for bugs. The reason for (1) is the fact that copy inside user pages are performed with the ldm instruction which has no mean for testing user protections and could possibly race with process preemption bypassing the COW mechanism for example. This is a longstanding issue that we said ought to be fixed for about two years now. The solution is to substitute those ldm insns with a series of ldrt or strt insns to enforce user memory protection. At least on StrongARM and XScale cores the ldm is not faster than the equivalent ldr/str insns with a warm i-cache so there is no measurable performance degradation with that change. The fact that the copy code is a template makes it pretty easy to reuse the same core code as for memcpy and benefit from the same performance optimizations. Now (2) is best demonstrated with actual throughput measurements. First, here is a summary of memcopy tests performed on a StrongARM core: PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 59.73 107.43 unaligned 32 61.31 74.72 aligned 100 132.47 136.15 unaligned 100 103.84 123.76 aligned 4096 130.67 130.80 unaligned 4096 130.68 130.64 aligned 1048576 68.03 68.18 unaligned 1048576 68.03 68.18 The buffer size is in bytes and the measured speed in MB/s. The copy was performed repeatedly with given buffer and throughput averaged over 3 seconds. Here we can see that the current kernel version has a higher entry cost that shows up with small buffers. As buffer size grows both implementation converge to the same throughput. Now here's the exact same test performed on an XScale core (PXA255): PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 46.99 77.58 unaligned 32 53.61 59.59 aligned 100 107.19 136.59 unaligned 100 83.61 97.58 aligned 4096 129.13 129.98 unaligned 4096 128.36 128.53 aligned 1048576 53.76 59.41 unaligned 1048576 33.67 56.96 Again we can see the entry setup cost being higher for the current kernel before getting to the main copy loop. Then throughput results converge as long as the buffer remains in the cache. Then the 1MB case shows more differences probably due to better pld placement and/or less instruction interlocks in this proposed implementation. Disclaimer: The PXA system was running with slower clocks than the StrongARM system so trying to infer any conclusion by comparing those separate sets of results side by side would be completely inappropriate. So... What this patch does is to replace both memcpy and memmove with an implementation based on the provided copy code template. The memmove code is kept separate since it is used only if the memory areas involved do overlap in which case the code is a transposition of the template but with the copy occurring in the opposite direction (trying to fit that mode into the template turned it into a mess not worth it for memmove alone). And obviously both memcpy and memmove were tested with all kinds of pointer alignments and buffer sizes to exercise all code paths for correctness. The next patch will provide the now trivial replacement implementation copy_to_user and copy_from_user. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2005-11-01 22:52:23 +03:00
add pc, pc, ip
nop
ARM: 6006/1: ARM: Use the correct NOP size in memmove for Thumb-2 kernel builds When compiling the kernel to Thumb-2, using a 16-bit NOP in the memmove() implementation causes the preceding ADD PC instruction to branch incorrectly in the middle of a 32-bit LDR or STR instruction. The memmove() code is now similar to the memcpy() template. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2010-03-29 13:29:46 +04:00
W(nop)
Thumb-2: Implement the unified arch/arm/lib functions This patch adds the ARM/Thumb-2 unified support for the arch/arm/lib/* files. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2009-07-24 15:32:57 +04:00
W(str) r3, [r0, #-4]!
W(str) r4, [r0, #-4]!
W(str) r5, [r0, #-4]!
W(str) r6, [r0, #-4]!
W(str) r7, [r0, #-4]!
W(str) r8, [r0, #-4]!
W(str) lr, [r0, #-4]!
[ARM] 2947/1: copy template with new memcpy/memmove Patch from Nicolas Pitre This patch provides a new implementation for optimized memory copy functions on ARM. It is made of two levels: a template that consists of the core copy code and separate files that define macros to be used with the core code depending on the type of copy needed. This allows for best performances while sharing the same core for implementing memcpy(), copy_from_user() and copy_to_user() for instance. Two reasons for this work: 1) the current copy_to_user/copy_from_user implementation assumes no task switch will ever occur in the middle of each copied page making it completely unsafe with CONFIG_PREEMPT=y. 2) current copy implementations are measurably suboptimal and optimizing different implementations separately is a pain and more opportunities for bugs. The reason for (1) is the fact that copy inside user pages are performed with the ldm instruction which has no mean for testing user protections and could possibly race with process preemption bypassing the COW mechanism for example. This is a longstanding issue that we said ought to be fixed for about two years now. The solution is to substitute those ldm insns with a series of ldrt or strt insns to enforce user memory protection. At least on StrongARM and XScale cores the ldm is not faster than the equivalent ldr/str insns with a warm i-cache so there is no measurable performance degradation with that change. The fact that the copy code is a template makes it pretty easy to reuse the same core code as for memcpy and benefit from the same performance optimizations. Now (2) is best demonstrated with actual throughput measurements. First, here is a summary of memcopy tests performed on a StrongARM core: PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 59.73 107.43 unaligned 32 61.31 74.72 aligned 100 132.47 136.15 unaligned 100 103.84 123.76 aligned 4096 130.67 130.80 unaligned 4096 130.68 130.64 aligned 1048576 68.03 68.18 unaligned 1048576 68.03 68.18 The buffer size is in bytes and the measured speed in MB/s. The copy was performed repeatedly with given buffer and throughput averaged over 3 seconds. Here we can see that the current kernel version has a higher entry cost that shows up with small buffers. As buffer size grows both implementation converge to the same throughput. Now here's the exact same test performed on an XScale core (PXA255): PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 46.99 77.58 unaligned 32 53.61 59.59 aligned 100 107.19 136.59 unaligned 100 83.61 97.58 aligned 4096 129.13 129.98 unaligned 4096 128.36 128.53 aligned 1048576 53.76 59.41 unaligned 1048576 33.67 56.96 Again we can see the entry setup cost being higher for the current kernel before getting to the main copy loop. Then throughput results converge as long as the buffer remains in the cache. Then the 1MB case shows more differences probably due to better pld placement and/or less instruction interlocks in this proposed implementation. Disclaimer: The PXA system was running with slower clocks than the StrongARM system so trying to infer any conclusion by comparing those separate sets of results side by side would be completely inappropriate. So... What this patch does is to replace both memcpy and memmove with an implementation based on the provided copy code template. The memmove code is kept separate since it is used only if the memory areas involved do overlap in which case the code is a transposition of the template but with the copy occurring in the opposite direction (trying to fit that mode into the template turned it into a mess not worth it for memmove alone). And obviously both memcpy and memmove were tested with all kinds of pointer alignments and buffer sizes to exercise all code paths for correctness. The next patch will provide the now trivial replacement implementation copy_to_user and copy_from_user. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2005-11-01 22:52:23 +03:00
CALGN( bcs 2b )
7: ldmfd sp!, {r5 - r8}
8: movs r2, r2, lsl #31
ldrneb r3, [r1, #-1]!
ldrcsb r4, [r1, #-1]!
ldrcsb ip, [r1, #-1]
strneb r3, [r0, #-1]!
strcsb r4, [r0, #-1]!
strcsb ip, [r0, #-1]
ldmfd sp!, {r0, r4, pc}
9: cmp ip, #2
ldrgtb r3, [r1, #-1]!
ldrgeb r4, [r1, #-1]!
ldrb lr, [r1, #-1]!
strgtb r3, [r0, #-1]!
strgeb r4, [r0, #-1]!
subs r2, r2, ip
strb lr, [r0, #-1]!
blt 8b
ands ip, r1, #3
beq 1b
10: bic r1, r1, #3
cmp ip, #2
ldr r3, [r1, #0]
beq 17f
blt 18f
.macro backward_copy_shift push pull
subs r2, r2, #28
blt 14f
[ARM] cache align destination pointer when copying memory for some processors The implementation for memory copy functions on ARM had a (disabled) provision for aligning the source pointer before loading registers with data. Turns out that aligning the _destination_ pointer is much more useful, as the read side is already sufficiently helped with the use of preload. So this changes the definition of the CALGN() macro to target the destination pointer instead, and turns it on for Feroceon processors where the gain is very noticeable. Signed-off-by: Nicolas Pitre <nico@marvell.com> Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
2008-03-31 20:38:31 +04:00
CALGN( ands ip, r0, #31 )
[ARM] 2947/1: copy template with new memcpy/memmove Patch from Nicolas Pitre This patch provides a new implementation for optimized memory copy functions on ARM. It is made of two levels: a template that consists of the core copy code and separate files that define macros to be used with the core code depending on the type of copy needed. This allows for best performances while sharing the same core for implementing memcpy(), copy_from_user() and copy_to_user() for instance. Two reasons for this work: 1) the current copy_to_user/copy_from_user implementation assumes no task switch will ever occur in the middle of each copied page making it completely unsafe with CONFIG_PREEMPT=y. 2) current copy implementations are measurably suboptimal and optimizing different implementations separately is a pain and more opportunities for bugs. The reason for (1) is the fact that copy inside user pages are performed with the ldm instruction which has no mean for testing user protections and could possibly race with process preemption bypassing the COW mechanism for example. This is a longstanding issue that we said ought to be fixed for about two years now. The solution is to substitute those ldm insns with a series of ldrt or strt insns to enforce user memory protection. At least on StrongARM and XScale cores the ldm is not faster than the equivalent ldr/str insns with a warm i-cache so there is no measurable performance degradation with that change. The fact that the copy code is a template makes it pretty easy to reuse the same core code as for memcpy and benefit from the same performance optimizations. Now (2) is best demonstrated with actual throughput measurements. First, here is a summary of memcopy tests performed on a StrongARM core: PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 59.73 107.43 unaligned 32 61.31 74.72 aligned 100 132.47 136.15 unaligned 100 103.84 123.76 aligned 4096 130.67 130.80 unaligned 4096 130.68 130.64 aligned 1048576 68.03 68.18 unaligned 1048576 68.03 68.18 The buffer size is in bytes and the measured speed in MB/s. The copy was performed repeatedly with given buffer and throughput averaged over 3 seconds. Here we can see that the current kernel version has a higher entry cost that shows up with small buffers. As buffer size grows both implementation converge to the same throughput. Now here's the exact same test performed on an XScale core (PXA255): PTR alignment buffer size kernel version this version ------------------------------------------------------------ aligned 32 46.99 77.58 unaligned 32 53.61 59.59 aligned 100 107.19 136.59 unaligned 100 83.61 97.58 aligned 4096 129.13 129.98 unaligned 4096 128.36 128.53 aligned 1048576 53.76 59.41 unaligned 1048576 33.67 56.96 Again we can see the entry setup cost being higher for the current kernel before getting to the main copy loop. Then throughput results converge as long as the buffer remains in the cache. Then the 1MB case shows more differences probably due to better pld placement and/or less instruction interlocks in this proposed implementation. Disclaimer: The PXA system was running with slower clocks than the StrongARM system so trying to infer any conclusion by comparing those separate sets of results side by side would be completely inappropriate. So... What this patch does is to replace both memcpy and memmove with an implementation based on the provided copy code template. The memmove code is kept separate since it is used only if the memory areas involved do overlap in which case the code is a transposition of the template but with the copy occurring in the opposite direction (trying to fit that mode into the template turned it into a mess not worth it for memmove alone). And obviously both memcpy and memmove were tested with all kinds of pointer alignments and buffer sizes to exercise all code paths for correctness. The next patch will provide the now trivial replacement implementation copy_to_user and copy_from_user. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2005-11-01 22:52:23 +03:00
CALGN( sbcnes r4, ip, r2 ) @ C is always set here
CALGN( subcc r2, r2, ip )
CALGN( bcc 15f )
11: stmfd sp!, {r5 - r9}
PLD( pld [r1, #-4] )
PLD( subs r2, r2, #96 )
PLD( pld [r1, #-32] )
PLD( blt 13f )
PLD( pld [r1, #-64] )
PLD( pld [r1, #-96] )
12: PLD( pld [r1, #-128] )
13: ldmdb r1!, {r7, r8, r9, ip}
mov lr, r3, push #\push
subs r2, r2, #32
ldmdb r1!, {r3, r4, r5, r6}
orr lr, lr, ip, pull #\pull
mov ip, ip, push #\push
orr ip, ip, r9, pull #\pull
mov r9, r9, push #\push
orr r9, r9, r8, pull #\pull
mov r8, r8, push #\push
orr r8, r8, r7, pull #\pull
mov r7, r7, push #\push
orr r7, r7, r6, pull #\pull
mov r6, r6, push #\push
orr r6, r6, r5, pull #\pull
mov r5, r5, push #\push
orr r5, r5, r4, pull #\pull
mov r4, r4, push #\push
orr r4, r4, r3, pull #\pull
stmdb r0!, {r4 - r9, ip, lr}
bge 12b
PLD( cmn r2, #96 )
PLD( bge 13b )
ldmfd sp!, {r5 - r9}
14: ands ip, r2, #28
beq 16f
15: mov lr, r3, push #\push
ldr r3, [r1, #-4]!
subs ip, ip, #4
orr lr, lr, r3, pull #\pull
str lr, [r0, #-4]!
bgt 15b
CALGN( cmp r2, #0 )
CALGN( bge 11b )
16: add r1, r1, #(\pull / 8)
b 8b
.endm
backward_copy_shift push=8 pull=24
17: backward_copy_shift push=16 pull=16
18: backward_copy_shift push=24 pull=8
[ARM] 5227/1: Add the ENDPROC declarations to the .S files This declaration specifies the "function" type and size for various assembly functions, mainly needed for generating the correct branch instructions in Thumb-2. Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2008-08-28 14:22:32 +04:00
ENDPROC(memmove)