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authorHannes Frederic Sowa <hannes@stressinduktion.org>2014-11-05 00:23:04 +0100
committerDavid S. Miller <davem@davemloft.net>2014-11-05 22:01:21 -0500
commite5a2c899957659cd1a9f789bc462f9c0b35f5150 (patch)
tree4c9b8a6f89d961daf9ada9f5ee95f8b371ce3a04 /lib
parent2c99cd914d4fed9160d98849c9dd38034616768e (diff)
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>
Diffstat (limited to 'lib')
-rw-r--r--lib/Makefile2
-rw-r--r--lib/hash.c39
2 files changed, 1 insertions, 40 deletions
diff --git a/lib/Makefile b/lib/Makefile
index 7512dc978f18..04e53dd16070 100644
--- 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
index fea973f4bd57..000000000000
--- 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);

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