diff options
author | Jason Baron <jbaron@redhat.com> | 2011-03-16 17:29:47 -0400 |
---|---|---|
committer | Steven Rostedt <rostedt@goodmis.org> | 2011-04-04 12:48:08 -0400 |
commit | d430d3d7e646eb1eac2bb4aa244a644312e67c76 (patch) | |
tree | 0f52534f54d89e41042536ff2f1b2ce74c45c033 /arch/x86/include/asm/jump_label.h | |
parent | ee5e51f51be755830f57445e268ba50e88ccbdbb (diff) |
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 <a.p.zijlstra@chello.nl>
LKML-Reference: <20110316212947.GA8792@redhat.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Suggested-by: H. Peter Anvin <hpa@linux.intel.com>
Tested-by: David Daney <ddaney@caviumnetworks.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'arch/x86/include/asm/jump_label.h')
-rw-r--r-- | arch/x86/include/asm/jump_label.h | 26 |
1 files changed, 15 insertions, 11 deletions
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h index 574dbc22893a..f217cee86533 100644 --- a/arch/x86/include/asm/jump_label.h +++ b/arch/x86/include/asm/jump_label.h | |||
@@ -5,20 +5,24 @@ | |||
5 | 5 | ||
6 | #include <linux/types.h> | 6 | #include <linux/types.h> |
7 | #include <asm/nops.h> | 7 | #include <asm/nops.h> |
8 | #include <asm/asm.h> | ||
8 | 9 | ||
9 | #define JUMP_LABEL_NOP_SIZE 5 | 10 | #define JUMP_LABEL_NOP_SIZE 5 |
10 | 11 | ||
11 | # define JUMP_LABEL_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t" | 12 | #define JUMP_LABEL_INITIAL_NOP ".byte 0xe9 \n\t .long 0\n\t" |
12 | 13 | ||
13 | # define JUMP_LABEL(key, label) \ | 14 | static __always_inline bool arch_static_branch(struct jump_label_key *key) |
14 | do { \ | 15 | { |
15 | asm goto("1:" \ | 16 | asm goto("1:" |
16 | JUMP_LABEL_INITIAL_NOP \ | 17 | JUMP_LABEL_INITIAL_NOP |
17 | ".pushsection __jump_table, \"aw\" \n\t"\ | 18 | ".pushsection __jump_table, \"aw\" \n\t" |
18 | _ASM_PTR "1b, %l[" #label "], %c0 \n\t" \ | 19 | _ASM_PTR "1b, %l[l_yes], %c0 \n\t" |
19 | ".popsection \n\t" \ | 20 | ".popsection \n\t" |
20 | : : "i" (key) : : label); \ | 21 | : : "i" (key) : : l_yes); |
21 | } while (0) | 22 | return false; |
23 | l_yes: | ||
24 | return true; | ||
25 | } | ||
22 | 26 | ||
23 | #endif /* __KERNEL__ */ | 27 | #endif /* __KERNEL__ */ |
24 | 28 | ||