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 --- include/asm-generic/hash.h | 36 ++++++++++++++++++++++++++++++++++-- 1 file changed, 34 insertions(+), 2 deletions(-) (limited to 'include/asm-generic') diff --git a/include/asm-generic/hash.h b/include/asm-generic/hash.h index b6312843dbd9..3c82760ff2a4 100644 --- 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 + +/** + * 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 */ -- cgit v1.2.3 From a77f9c5dcdf8480a93332792c336fa2bf9d31229 Mon Sep 17 00:00:00 2001 From: Jay Vosburgh Date: Fri, 14 Nov 2014 11:05:06 -0800 Subject: Revert "fast_hash: avoid indirect function calls" This reverts commit e5a2c899957659cd1a9f789bc462f9c0b35f5150. Commit e5a2c899 introduced an alternative_call, arch_fast_hash2, that selects between __jhash2 and __intel_crc4_2_hash based on the X86_FEATURE_XMM4_2. Unfortunately, the alternative_call system does not appear to be suitable for use with C functions, as register usage is not handled properly for the called functions. The __jhash2 function in particular clobbers registers that are not preserved when called via alternative_call, resulting in a panic for direct callers of arch_fast_hash2 on older CPUs lacking sse4_2. It is possible that __intel_crc4_2_hash works merely by chance because it uses fewer registers. This commit was suggested as the source of the problem by Jesse Gross . Signed-off-by: Jay Vosburgh Signed-off-by: David S. Miller --- include/asm-generic/hash.h | 36 ++---------------------------------- 1 file changed, 2 insertions(+), 34 deletions(-) (limited to 'include/asm-generic') diff --git a/include/asm-generic/hash.h b/include/asm-generic/hash.h index 3c82760ff2a4..b6312843dbd9 100644 --- a/include/asm-generic/hash.h +++ b/include/asm-generic/hash.h @@ -1,41 +1,9 @@ #ifndef __ASM_GENERIC_HASH_H #define __ASM_GENERIC_HASH_H -#include - -/** - * 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) +struct fast_hash_ops; +static inline void setup_arch_fast_hash(struct fast_hash_ops *ops) { - return jhash2(data, len, seed); } #endif /* __ASM_GENERIC_HASH_H */ -- cgit v1.2.3 From 0cb6c969ed9de43687abdfc63714b6fe4385d2fc Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Wed, 10 Dec 2014 16:33:12 +0100 Subject: net, lib: kill arch_fast_hash library bits As there are now no remaining users of arch_fast_hash(), lets kill it entirely. This basically reverts commit 71ae8aac3e19 ("lib: introduce arch optimized hash library") and follow-up work, that is f.e., commit 237217546d44 ("lib: hash: follow-up fixups for arch hash"), commit e3fec2f74f7f ("lib: Add missing arch generic-y entries for asm-generic/hash.h") and last but not least commit 6a02652df511 ("perf tools: Fix include for non x86 architectures"). Cc: Francesco Fusco Cc: Thomas Graf Cc: Arnaldo Carvalho de Melo Signed-off-by: Daniel Borkmann Signed-off-by: David S. Miller --- include/asm-generic/hash.h | 9 --------- 1 file changed, 9 deletions(-) delete mode 100644 include/asm-generic/hash.h (limited to 'include/asm-generic') diff --git a/include/asm-generic/hash.h b/include/asm-generic/hash.h deleted file mode 100644 index b6312843dbd9..000000000000 --- a/include/asm-generic/hash.h +++ /dev/null @@ -1,9 +0,0 @@ -#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) -{ -} - -#endif /* __ASM_GENERIC_HASH_H */ -- cgit v1.2.3