From d430d3d7e646eb1eac2bb4aa244a644312e67c76 Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Wed, 16 Mar 2011 17:29:47 -0400 Subject: jump label: Introduce static_branch() interface Introduce: static __always_inline bool static_branch(struct jump_label_key *key); instead of the old JUMP_LABEL(key, label) macro. In this way, jump labels become really easy to use: Define: struct jump_label_key jump_key; Can be used as: if (static_branch(&jump_key)) do unlikely code enable/disale via: jump_label_inc(&jump_key); jump_label_dec(&jump_key); that's it! For the jump labels disabled case, the static_branch() becomes an atomic_read(), and jump_label_inc()/dec() are simply atomic_inc(), atomic_dec() operations. We show testing results for this change below. Thanks to H. Peter Anvin for suggesting the 'static_branch()' construct. Since we now require a 'struct jump_label_key *key', we can store a pointer into the jump table addresses. In this way, we can enable/disable jump labels, in basically constant time. This change allows us to completely remove the previous hashtable scheme. Thanks to Peter Zijlstra for this re-write. Testing: I ran a series of 'tbench 20' runs 5 times (with reboots) for 3 configurations, where tracepoints were disabled. jump label configured in avg: 815.6 jump label *not* configured in (using atomic reads) avg: 800.1 jump label *not* configured in (regular reads) avg: 803.4 Signed-off-by: Peter Zijlstra LKML-Reference: <20110316212947.GA8792@redhat.com> Signed-off-by: Jason Baron Suggested-by: H. Peter Anvin Tested-by: David Daney Acked-by: Ralf Baechle Acked-by: David S. Miller Acked-by: Mathieu Desnoyers Signed-off-by: Steven Rostedt --- arch/mips/include/asm/jump_label.h | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) (limited to 'arch/mips/include/asm') diff --git a/arch/mips/include/asm/jump_label.h b/arch/mips/include/asm/jump_label.h index 7622ccf75076..1881b316ca45 100644 --- a/arch/mips/include/asm/jump_label.h +++ b/arch/mips/include/asm/jump_label.h @@ -20,16 +20,18 @@ #define WORD_INSN ".word" #endif -#define JUMP_LABEL(key, label) \ - do { \ - asm goto("1:\tnop\n\t" \ - "nop\n\t" \ - ".pushsection __jump_table, \"a\"\n\t" \ - WORD_INSN " 1b, %l[" #label "], %0\n\t" \ - ".popsection\n\t" \ - : : "i" (key) : : label); \ - } while (0) - +static __always_inline bool arch_static_branch(struct jump_label_key *key) +{ + asm goto("1:\tnop\n\t" + "nop\n\t" + ".pushsection __jump_table, \"aw\"\n\t" + WORD_INSN " 1b, %l[l_yes], %0\n\t" + ".popsection\n\t" + : : "i" (key) : : l_yes); + return false; +l_yes: + return true; +} #endif /* __KERNEL__ */ -- cgit v1.2.3