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Date: Thu, 1 Aug 2013 15:55:07 -0400
From: Ken Steele <ken@...era.com>
To: <linux-kernel@...r.kernel.org>
Subject: [PATCH v2] tile: optimize strnlen using SIMD instructions
Using strlen as a model, add length checking to create strnlen.
Signed-off-by: Ken Steele <ken@...era.com>
Signed-off-by: Chris Metcalf <cmetcalf@...era.com>
---
v2 of the patch adds an "& 31" to the shift count for 32-bit strnlen.
It turns out this doesn't affect the generated code at all, and it's
technically more correct, as pointed out by Max Filippov <jcmvbkbc@...il.com>.
arch/tile/include/asm/string.h | 2 ++
arch/tile/lib/Makefile | 2 +-
arch/tile/lib/strnlen_32.c | 47 +++++++++++++++++++++++++++++++++++++++++
arch/tile/lib/strnlen_64.c | 48 ++++++++++++++++++++++++++++++++++++++++++
4 files changed, 98 insertions(+), 1 deletion(-)
create mode 100644 arch/tile/lib/strnlen_32.c
create mode 100644 arch/tile/lib/strnlen_64.c
diff --git a/arch/tile/include/asm/string.h b/arch/tile/include/asm/string.h
index 7535cf1..92b271b 100644
--- a/arch/tile/include/asm/string.h
+++ b/arch/tile/include/asm/string.h
@@ -21,8 +21,10 @@
#define __HAVE_ARCH_MEMMOVE
#define __HAVE_ARCH_STRCHR
#define __HAVE_ARCH_STRLEN
+#define __HAVE_ARCH_STRNLEN
extern __kernel_size_t strlen(const char *);
+extern __kernel_size_t strnlen(const char *, __kernel_size_t);
extern char *strchr(const char *s, int c);
extern void *memchr(const void *s, int c, size_t n);
extern void *memset(void *, int, __kernel_size_t);
diff --git a/arch/tile/lib/Makefile b/arch/tile/lib/Makefile
index 985f598..5d84437 100644
--- a/arch/tile/lib/Makefile
+++ b/arch/tile/lib/Makefile
@@ -4,7 +4,7 @@
lib-y = cacheflush.o checksum.o cpumask.o delay.o uaccess.o \
memmove.o memcpy_$(BITS).o memchr_$(BITS).o memset_$(BITS).o \
- strchr_$(BITS).o strlen_$(BITS).o
+ strchr_$(BITS).o strlen_$(BITS).o strnlen_$(BITS).o
ifeq ($(CONFIG_TILEGX),y)
CFLAGS_REMOVE_memcpy_user_64.o = -fno-omit-frame-pointer
diff --git a/arch/tile/lib/strnlen_32.c b/arch/tile/lib/strnlen_32.c
new file mode 100644
index 0000000..1434141
--- /dev/null
+++ b/arch/tile/lib/strnlen_32.c
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2013 Tilera Corporation. All Rights Reserved.
+ *
+ * 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, version 2.
+ *
+ * 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, GOOD TITLE or
+ * NON INFRINGEMENT. See the GNU General Public License for
+ * more details.
+ */
+
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/module.h>
+
+size_t strnlen(const char *s, size_t count)
+{
+ /* Get an aligned pointer. */
+ const uintptr_t s_int = (uintptr_t) s;
+ const uint32_t *p = (const uint32_t *)(s_int & -4);
+ size_t bytes_read = sizeof(*p) - (s_int & (sizeof(*p) - 1));
+ size_t len;
+ uint32_t v, bits;
+
+ /* Avoid page fault risk by not reading any bytes when count is 0. */
+ if (count == 0)
+ return 0;
+
+ /* Read first word, but force bytes before the string to be nonzero. */
+ v = *p | ((1 << ((s_int << 3) & 31)) - 1);
+
+ while ((bits = __insn_seqb(v, 0)) == 0) {
+ if (bytes_read >= count) {
+ /* Read COUNT bytes and didn't find the terminator. */
+ return count;
+ }
+ v = *++p;
+ bytes_read += sizeof(v);
+ }
+
+ len = ((const char *) p) + (__insn_ctz(bits) >> 3) - s;
+ return (len < count ? len : count);
+}
+EXPORT_SYMBOL(strnlen);
diff --git a/arch/tile/lib/strnlen_64.c b/arch/tile/lib/strnlen_64.c
new file mode 100644
index 0000000..2e8de6a
--- /dev/null
+++ b/arch/tile/lib/strnlen_64.c
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2013 Tilera Corporation. All Rights Reserved.
+ *
+ * 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, version 2.
+ *
+ * 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, GOOD TITLE or
+ * NON INFRINGEMENT. See the GNU General Public License for
+ * more details.
+ */
+
+#include <linux/types.h>
+#include <linux/string.h>
+#include <linux/module.h>
+#include "string-endian.h"
+
+size_t strnlen(const char *s, size_t count)
+{
+ /* Get an aligned pointer. */
+ const uintptr_t s_int = (uintptr_t) s;
+ const uint64_t *p = (const uint64_t *)(s_int & -8);
+ size_t bytes_read = sizeof(*p) - (s_int & (sizeof(*p) - 1));
+ size_t len;
+ uint64_t v, bits;
+
+ /* Avoid page fault risk by not reading any bytes when count is 0. */
+ if (count == 0)
+ return 0;
+
+ /* Read and MASK the first word. */
+ v = *p | MASK(s_int);
+
+ while ((bits = __insn_v1cmpeqi(v, 0)) == 0) {
+ if (bytes_read >= count) {
+ /* Read COUNT bytes and didn't find the terminator. */
+ return count;
+ }
+ v = *++p;
+ bytes_read += sizeof(v);
+ }
+
+ len = ((const char *) p) + (CFZ(bits) >> 3) - s;
+ return (len < count ? len : count);
+}
+EXPORT_SYMBOL(strnlen);
--
1.8.3.1
--
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