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Subject[PATCH v6 1/2] powerpc/lib: optimise 32 bits __clear_user()
Date
Rewrite clear_user() on the same principle as memset(0), making use
of dcbz to clear complete cache lines.

This code is a copy/paste of memset(), with some modifications
in order to retrieve remaining number of bytes to be cleared,
as it needs to be returned in case of error.

On the same way as done on PPC64 in commit 17968fbbd19f1
("powerpc: 64bit optimised __clear_user"), the patch moves
__clear_user() into a dedicated file string_32.S

On a MPC885, throughput is almost doubled:

Before:
~# dd if=/dev/zero of=/dev/null bs=1M count=1000
1048576000 bytes (1000.0MB) copied, 18.990779 seconds, 52.7MB/s

After:
~# dd if=/dev/zero of=/dev/null bs=1M count=1000
1048576000 bytes (1000.0MB) copied, 9.611468 seconds, 104.0MB/s

On a MPC8321, throughput is multiplied by 2.12:

Before:
root@vgoippro:~# dd if=/dev/zero of=/dev/null bs=1M count=1000
1048576000 bytes (1000.0MB) copied, 6.844352 seconds, 146.1MB/s

After:
root@vgoippro:~# dd if=/dev/zero of=/dev/null bs=1M count=1000
1048576000 bytes (1000.0MB) copied, 3.218854 seconds, 310.7MB/s

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
arch/powerpc/lib/Makefile | 5 ++-
arch/powerpc/lib/string.S | 46 ----------------------
arch/powerpc/lib/string_32.S | 90 ++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 93 insertions(+), 48 deletions(-)
create mode 100644 arch/powerpc/lib/string_32.S

diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 653901042ad7..2c9b8c0adf22 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -26,13 +26,14 @@ obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o copypage_power7.o \
memcpy_power7.o

obj64-y += copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
- string_64.o memcpy_64.o memcmp_64.o pmem.o
+ memcpy_64.o memcmp_64.o pmem.o

obj64-$(CONFIG_SMP) += locks.o
obj64-$(CONFIG_ALTIVEC) += vmx-helper.o
obj64-$(CONFIG_KPROBES_SANITY_TEST) += test_emulate_step.o

-obj-y += checksum_$(BITS).o checksum_wrappers.o
+obj-y += checksum_$(BITS).o checksum_wrappers.o \
+ string_$(BITS).o

obj-y += sstep.o ldstfp.o quad.o
obj64-y += quad.o
diff --git a/arch/powerpc/lib/string.S b/arch/powerpc/lib/string.S
index 0378def28d41..5343a88e619e 100644
--- a/arch/powerpc/lib/string.S
+++ b/arch/powerpc/lib/string.S
@@ -8,8 +8,6 @@
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
-#include <asm/processor.h>
-#include <asm/errno.h>
#include <asm/ppc_asm.h>
#include <asm/export.h>
#include <asm/cache.h>
@@ -86,47 +84,3 @@ _GLOBAL(memchr)
2: li r3,0
blr
EXPORT_SYMBOL(memchr)
-
-#ifdef CONFIG_PPC32
-_GLOBAL(__clear_user)
- addi r6,r3,-4
- li r3,0
- li r5,0
- cmplwi 0,r4,4
- blt 7f
- /* clear a single word */
-11: stwu r5,4(r6)
- beqlr
- /* clear word sized chunks */
- andi. r0,r6,3
- add r4,r0,r4
- subf r6,r0,r6
- srwi r0,r4,2
- andi. r4,r4,3
- mtctr r0
- bdz 7f
-1: stwu r5,4(r6)
- bdnz 1b
- /* clear byte sized chunks */
-7: cmpwi 0,r4,0
- beqlr
- mtctr r4
- addi r6,r6,3
-8: stbu r5,1(r6)
- bdnz 8b
- blr
-90: mr r3,r4
- blr
-91: mfctr r3
- slwi r3,r3,2
- add r3,r3,r4
- blr
-92: mfctr r3
- blr
-
- EX_TABLE(11b, 90b)
- EX_TABLE(1b, 91b)
- EX_TABLE(8b, 92b)
-
-EXPORT_SYMBOL(__clear_user)
-#endif
diff --git a/arch/powerpc/lib/string_32.S b/arch/powerpc/lib/string_32.S
new file mode 100644
index 000000000000..6de67d2dbad6
--- /dev/null
+++ b/arch/powerpc/lib/string_32.S
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * String handling functions for PowerPC32
+ *
+ * Copyright (C) 1996 Paul Mackerras.
+ *
+ */
+
+#include <asm/ppc_asm.h>
+#include <asm/export.h>
+#include <asm/cache.h>
+
+ .text
+
+CACHELINE_BYTES = L1_CACHE_BYTES
+LG_CACHELINE_BYTES = L1_CACHE_SHIFT
+CACHELINE_MASK = (L1_CACHE_BYTES-1)
+
+_GLOBAL(__clear_user)
+/*
+ * Use dcbz on the complete cache lines in the destination
+ * to set them to zero. This requires that the destination
+ * area is cacheable.
+ */
+ cmplwi cr0, r4, 4
+ mr r10, r3
+ li r3, 0
+ blt 7f
+
+11: stw r3, 0(r10)
+ beqlr
+ andi. r0, r10, 3
+ add r11, r0, r4
+ subf r6, r0, r10
+
+ clrlwi r7, r6, 32 - LG_CACHELINE_BYTES
+ add r8, r7, r11
+ srwi r9, r8, LG_CACHELINE_BYTES
+ addic. r9, r9, -1 /* total number of complete cachelines */
+ ble 2f
+ xori r0, r7, CACHELINE_MASK & ~3
+ srwi. r0, r0, 2
+ beq 3f
+ mtctr r0
+4: stwu r3, 4(r6)
+ bdnz 4b
+3: mtctr r9
+ li r7, 4
+10: dcbz r7, r6
+ addi r6, r6, CACHELINE_BYTES
+ bdnz 10b
+ clrlwi r11, r8, 32 - LG_CACHELINE_BYTES
+ addi r11, r11, 4
+
+2: srwi r0 ,r11 ,2
+ mtctr r0
+ bdz 6f
+1: stwu r3, 4(r6)
+ bdnz 1b
+6: andi. r11, r11, 3
+ beqlr
+ mtctr r11
+ addi r6, r6, 3
+8: stbu r3, 1(r6)
+ bdnz 8b
+ blr
+
+7: cmpwi cr0, r4, 0
+ beqlr
+ mtctr r4
+ addi r6, r10, -1
+9: stbu r3, 1(r6)
+ bdnz 9b
+ blr
+
+90: mr r3, r4
+ blr
+91: add r3, r10, r4
+ subf r3, r6, r3
+ blr
+
+ EX_TABLE(11b, 90b)
+ EX_TABLE(4b, 91b)
+ EX_TABLE(10b, 91b)
+ EX_TABLE(1b, 91b)
+ EX_TABLE(8b, 91b)
+ EX_TABLE(9b, 91b)
+
+EXPORT_SYMBOL(__clear_user)
--
2.13.3
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