From e5a2c899957659cd1a9f789bc462f9c0b35f5150 Mon Sep 17 00:00:00 2001 From: Hannes Frederic Sowa Date: Wed, 5 Nov 2014 00:23:04 +0100 Subject: 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 Cc: Thomas Graf Signed-off-by: Hannes Frederic Sowa Signed-off-by: David S. Miller --- lib/Makefile | 2 +- lib/hash.c | 39 --------------------------------------- 2 files changed, 1 insertion(+), 40 deletions(-) delete mode 100644 lib/hash.c (limited to 'lib') 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 - * Copyright 2013 Daniel Borkmann - * Copyright 2013 Thomas Graf - * Licensed under the GNU General Public License, version 2.0 (GPLv2) - */ - -#include -#include -#include - -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); -- cgit v1.2.3-58-ga151