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jump label: Introduce static_branch() interface

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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>
This commit is contained in:
Jason Baron 2011-03-16 17:29:47 -04:00 • committed by Steven Rostedt
parent ee5e51f51b
commit d430d3d7e6
15 changed files with 416 additions and 546 deletions
Download patch file Download diff file Expand all files Collapse all files

23
kernel/tracepoint.c
View file

@ -251,9 +251,9 @@ static void set_tracepoint(struct tracepoint_entry **entry,
{
WARN_ON(strcmp((*entry)->name, elem->name) != 0);
if (elem->regfunc && !elem->state && active)
if (elem->regfunc && !jump_label_enabled(&elem->key) && active)
elem->regfunc();
else if (elem->unregfunc && elem->state && !active)
else if (elem->unregfunc && jump_label_enabled(&elem->key) && !active)
elem->unregfunc();
/*
@ -264,13 +264,10 @@ static void set_tracepoint(struct tracepoint_entry **entry,
* is used.
*/
rcu_assign_pointer(elem->funcs, (*entry)->funcs);
if (!elem->state && active) {
jump_label_enable(&elem->state);
elem->state = active;
} else if (elem->state && !active) {
jump_label_disable(&elem->state);
elem->state = active;
}
if (active && !jump_label_enabled(&elem->key))
jump_label_inc(&elem->key);
else if (!active && jump_label_enabled(&elem->key))
jump_label_dec(&elem->key);
}
/*
@ -281,13 +278,11 @@ static void set_tracepoint(struct tracepoint_entry **entry,
*/
static void disable_tracepoint(struct tracepoint *elem)
{
if (elem->unregfunc && elem->state)
if (elem->unregfunc && jump_label_enabled(&elem->key))
elem->unregfunc();
if (elem->state) {
jump_label_disable(&elem->state);
elem->state = 0;
}
if (jump_label_enabled(&elem->key))
jump_label_dec(&elem->key);
rcu_assign_pointer(elem->funcs, NULL);
}