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 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'lib/Makefile') 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-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o obj-y += kstrtox.o -- cgit v1.2.3 From a77f9c5dcdf8480a93332792c336fa2bf9d31229 Mon Sep 17 00:00:00 2001 From: Jay Vosburgh Date: Fri, 14 Nov 2014 11:05:06 -0800 Subject: Revert "fast_hash: avoid indirect function calls" This reverts commit e5a2c899957659cd1a9f789bc462f9c0b35f5150. Commit e5a2c899 introduced an alternative_call, arch_fast_hash2, that selects between __jhash2 and __intel_crc4_2_hash based on the X86_FEATURE_XMM4_2. Unfortunately, the alternative_call system does not appear to be suitable for use with C functions, as register usage is not handled properly for the called functions. The __jhash2 function in particular clobbers registers that are not preserved when called via alternative_call, resulting in a panic for direct callers of arch_fast_hash2 on older CPUs lacking sse4_2. It is possible that __intel_crc4_2_hash works merely by chance because it uses fewer registers. This commit was suggested as the source of the problem by Jesse Gross . Signed-off-by: Jay Vosburgh Signed-off-by: David S. Miller --- lib/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'lib/Makefile') diff --git a/lib/Makefile b/lib/Makefile index 04e53dd16070..7512dc978f18 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -26,7 +26,7 @@ obj-y += bcd.o div64.o sort.o parser.o halfmd4.o debug_locks.o random32.o \ bust_spinlocks.o hexdump.o kasprintf.o bitmap.o scatterlist.o \ gcd.o lcm.o list_sort.o uuid.o flex_array.o iovec.o clz_ctz.o \ bsearch.o find_last_bit.o find_next_bit.o llist.o memweight.o kfifo.o \ - percpu-refcount.o percpu_ida.o rhashtable.o + percpu-refcount.o percpu_ida.o hash.o rhashtable.o obj-y += string_helpers.o obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o obj-y += kstrtox.o -- 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 --- lib/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'lib/Makefile') diff --git a/lib/Makefile b/lib/Makefile index 0211d2bd5e17..4b9baa45a4d9 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 reciprocal_div.o + percpu-refcount.o percpu_ida.o rhashtable.o reciprocal_div.o obj-y += string_helpers.o obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o obj-y += kstrtox.o -- cgit v1.2.3