jump label: Introduce static_branch() interface
authorJason Baron <jbaron@redhat.com>
Wed, 16 Mar 2011 21:29:47 +0000 (17:29 -0400)
committerSteven Rostedt <rostedt@goodmis.org>
Mon, 4 Apr 2011 16:48:08 +0000 (12:48 -0400)
commitd430d3d7e646eb1eac2bb4aa244a644312e67c76
tree0f52534f54d89e41042536ff2f1b2ce74c45c033
parentee5e51f51be755830f57445e268ba50e88ccbdbb
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>
15 files changed:
arch/mips/include/asm/jump_label.h
arch/sparc/include/asm/jump_label.h
arch/x86/include/asm/alternative.h
arch/x86/include/asm/jump_label.h
arch/x86/kernel/alternative.c
arch/x86/kernel/module.c
include/asm-generic/vmlinux.lds.h
include/linux/dynamic_debug.h
include/linux/jump_label.h
include/linux/jump_label_ref.h [deleted file]
include/linux/perf_event.h
include/linux/tracepoint.h
kernel/jump_label.c
kernel/perf_event.c
kernel/tracepoint.c