fast_hash: avoid indirect function calls

By default the arch_fast_hash hashing function pointers are initialized
to jhash(2). If during boot-up a CPU with SSE4.2 is detected they get
updated to the CRC32 ones. This dispatching scheme incurs a function
pointer lookup and indirect call for every hashing operation.

rhashtable as a user of arch_fast_hash e.g. stores pointers to hashing
functions in its structure, too, causing two indirect branches per
hashing operation.

Using alternative_call we can get away with one of those indirect branches.

Acked-by: Daniel Borkmann <dborkman@redhat.com>
Cc: Thomas Graf <tgraf@suug.ch>
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/arch/x86/include/asm/hash.h b/arch/x86/include/asm/hash.h
index e8c58f8..a881d78 100644 (file)
--- a/arch/x86/include/asm/hash.h
+++ b/arch/x86/include/asm/hash.h
@@ -1,7 +1,48 @@
-#ifndef _ASM_X86_HASH_H
-#define _ASM_X86_HASH_H
+#ifndef __ASM_X86_HASH_H
+#define __ASM_X86_HASH_H
 
-struct fast_hash_ops;
-extern void setup_arch_fast_hash(struct fast_hash_ops *ops);
+#include <linux/cpufeature.h>
+#include <asm/alternative.h>
 
-#endif /* _ASM_X86_HASH_H */
+u32 __intel_crc4_2_hash(const void *data, u32 len, u32 seed);
+u32 __intel_crc4_2_hash2(const u32 *data, u32 len, u32 seed);
+
+/*
+ * non-inline versions of jhash so gcc does not need to generate
+ * duplicate code in every object file
+ */
+u32 __jhash(const void *data, u32 len, u32 seed);
+u32 __jhash2(const u32 *data, u32 len, u32 seed);
+
+/*
+ * for documentation of these functions please look into
+ * <include/asm-generic/hash.h>
+ */
+
+static inline u32 arch_fast_hash(const void *data, u32 len, u32 seed)
+{
+       u32 hash;
+
+       alternative_call(__jhash, __intel_crc4_2_hash, X86_FEATURE_XMM4_2,
+#ifdef CONFIG_X86_64
+                        "=a" (hash), "D" (data), "S" (len), "d" (seed));
+#else
+                        "=a" (hash), "a" (data), "d" (len), "c" (seed));
+#endif
+       return hash;
+}
+
+static inline u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
+{
+       u32 hash;
+
+       alternative_call(__jhash2, __intel_crc4_2_hash2, X86_FEATURE_XMM4_2,
+#ifdef CONFIG_X86_64
+                        "=a" (hash), "D" (data), "S" (len), "d" (seed));
+#else
+                        "=a" (hash), "a" (data), "d" (len), "c" (seed));
+#endif
+       return hash;
+}
+
+#endif /* __ASM_X86_HASH_H */

diff --git a/arch/x86/lib/hash.c b/arch/x86/lib/hash.c
index ff4fa51..e143271 100644 (file)
--- a/arch/x86/lib/hash.c
+++ b/arch/x86/lib/hash.c
@@ -31,13 +31,13 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <linux/hash.h>
-#include <linux/init.h>
-
 #include <asm/processor.h>
 #include <asm/cpufeature.h>
 #include <asm/hash.h>
 
+#include <linux/hash.h>
+#include <linux/jhash.h>
+
 static inline u32 crc32_u32(u32 crc, u32 val)
 {
 #ifdef CONFIG_AS_CRC32
@@ -48,7 +48,7 @@ static inline u32 crc32_u32(u32 crc, u32 val)
        return crc;
 }
 
-static u32 intel_crc4_2_hash(const void *data, u32 len, u32 seed)
+u32 __intel_crc4_2_hash(const void *data, u32 len, u32 seed)
 {
        const u32 *p32 = (const u32 *) data;
        u32 i, tmp = 0;
@@ -71,22 +71,27 @@ static u32 intel_crc4_2_hash(const void *data, u32 len, u32 seed)
 
        return seed;
 }
+EXPORT_SYMBOL(__intel_crc4_2_hash);
 
-static u32 intel_crc4_2_hash2(const u32 *data, u32 len, u32 seed)
+u32 __intel_crc4_2_hash2(const u32 *data, u32 len, u32 seed)
 {
-       const u32 *p32 = (const u32 *) data;
        u32 i;
 
        for (i = 0; i < len; i++)
-               seed = crc32_u32(seed, *p32++);
+               seed = crc32_u32(seed, *data++);
 
        return seed;
 }
+EXPORT_SYMBOL(__intel_crc4_2_hash2);
 
-void __init setup_arch_fast_hash(struct fast_hash_ops *ops)
+u32 __jhash(const void *data, u32 len, u32 seed)
 {
-       if (cpu_has_xmm4_2) {
-               ops->hash  = intel_crc4_2_hash;
-               ops->hash2 = intel_crc4_2_hash2;
-       }
+       return jhash(data, len, seed);
+}
+EXPORT_SYMBOL(__jhash);
+
+u32 __jhash2(const u32 *data, u32 len, u32 seed)
+{
+       return jhash2(data, len, seed);
 }
+EXPORT_SYMBOL(__jhash2);

diff --git a/include/asm-generic/hash.h b/include/asm-generic/hash.h
index b631284..3c82760 100644 (file)
--- a/include/asm-generic/hash.h
+++ b/include/asm-generic/hash.h
@@ -1,9 +1,41 @@
 #ifndef __ASM_GENERIC_HASH_H
 #define __ASM_GENERIC_HASH_H
 
-struct fast_hash_ops;
-static inline void setup_arch_fast_hash(struct fast_hash_ops *ops)
+#include <linux/jhash.h>
+
+/**
+ *     arch_fast_hash - Caclulates a hash over a given buffer that can have
+ *                      arbitrary size. This function will eventually use an
+ *                      architecture-optimized hashing implementation if
+ *                      available, and trades off distribution for speed.
+ *
+ *     @data: buffer to hash
+ *     @len: length of buffer in bytes
+ *     @seed: start seed
+ *
+ *     Returns 32bit hash.
+ */
+static inline u32 arch_fast_hash(const void *data, u32 len, u32 seed)
+{
+       return jhash(data, len, seed);
+}
+
+/**
+ *     arch_fast_hash2 - Caclulates a hash over a given buffer that has a
+ *                       size that is of a multiple of 32bit words. This
+ *                       function will eventually use an architecture-
+ *                       optimized hashing implementation if available,
+ *                       and trades off distribution for speed.
+ *
+ *     @data: buffer to hash (must be 32bit padded)
+ *     @len: number of 32bit words
+ *     @seed: start seed
+ *
+ *     Returns 32bit hash.
+ */
+static inline u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
 {
+       return jhash2(data, len, seed);
 }
 
 #endif /* __ASM_GENERIC_HASH_H */

diff --git a/include/linux/hash.h b/include/linux/hash.h
index d0494c3..6e8fb02 100644 (file)
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -84,38 +84,4 @@ static inline u32 hash32_ptr(const void *ptr)
        return (u32)val;
 }
 
-struct fast_hash_ops {
-       u32 (*hash)(const void *data, u32 len, u32 seed);
-       u32 (*hash2)(const u32 *data, u32 len, u32 seed);
-};
-
-/**
- *     arch_fast_hash - Caclulates a hash over a given buffer that can have
- *                      arbitrary size. This function will eventually use an
- *                      architecture-optimized hashing implementation if
- *                      available, and trades off distribution for speed.
- *
- *     @data: buffer to hash
- *     @len: length of buffer in bytes
- *     @seed: start seed
- *
- *     Returns 32bit hash.
- */
-extern u32 arch_fast_hash(const void *data, u32 len, u32 seed);
-
-/**
- *     arch_fast_hash2 - Caclulates a hash over a given buffer that has a
- *                       size that is of a multiple of 32bit words. This
- *                       function will eventually use an architecture-
- *                       optimized hashing implementation if available,
- *                       and trades off distribution for speed.
- *
- *     @data: buffer to hash (must be 32bit padded)
- *     @len: number of 32bit words
- *     @seed: start seed
- *
- *     Returns 32bit hash.
- */
-extern u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed);
-
 #endif /* _LINUX_HASH_H */

diff --git a/lib/Makefile b/lib/Makefile
index 7512dc9..04e53dd 100644 (file)
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \
         bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \
         gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \
         bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \
-        percpu-refcount.o percpu_ida.o hash.o rhashtable.o
+        percpu-refcount.o percpu_ida.o rhashtable.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
 obj-y += kstrtox.o

diff --git a/lib/hash.c b/lib/hash.c
deleted file mode 100644 (file)
index fea973f..0000000
--- a/lib/hash.c
+++ /dev/null
@@ -1,39 +0,0 @@
-/* General purpose hashing library
- *
- * That's a start of a kernel hashing library, which can be extended
- * with further algorithms in future. arch_fast_hash{2,}() will
- * eventually resolve to an architecture optimized implementation.
- *
- * Copyright 2013 Francesco Fusco <ffusco@redhat.com>
- * Copyright 2013 Daniel Borkmann <dborkman@redhat.com>
- * Copyright 2013 Thomas Graf <tgraf@redhat.com>
- * Licensed under the GNU General Public License, version 2.0 (GPLv2)
- */
-
-#include <linux/jhash.h>
-#include <linux/hash.h>
-#include <linux/cache.h>
-
-static struct fast_hash_ops arch_hash_ops __read_mostly = {
-       .hash  = jhash,
-       .hash2 = jhash2,
-};
-
-u32 arch_fast_hash(const void *data, u32 len, u32 seed)
-{
-       return arch_hash_ops.hash(data, len, seed);
-}
-EXPORT_SYMBOL_GPL(arch_fast_hash);
-
-u32 arch_fast_hash2(const u32 *data, u32 len, u32 seed)
-{
-       return arch_hash_ops.hash2(data, len, seed);
-}
-EXPORT_SYMBOL_GPL(arch_fast_hash2);
-
-static int __init hashlib_init(void)
-{
-       setup_arch_fast_hash(&arch_hash_ops);
-       return 0;
-}
-early_initcall(hashlib_init);