2017-08-21 23:43:53

by Eric Biggers

Subject: [PATCH] once: switch to new jump label API

From: Eric Biggers <[email protected]>

Switch the DO_ONCE() macro from the deprecated jump label API to the new
one. The new one is more readable, and for DO_ONCE() it also makes the
generated code more icache-friendly: now the one-time initialization
code is placed out-of-line at the jump target, rather than at the inline
fallthrough case.

Signed-off-by: Eric Biggers <[email protected]>
---
include/linux/once.h | 6 +++---
lib/once.c | 8 ++++----
2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/include/linux/once.h b/include/linux/once.h
index 9c98aaa87cbc..724724918e8b 100644
--- a/include/linux/once.h
+++ b/include/linux/once.h
@@ -5,7 +5,7 @@
#include <linux/jump_label.h>

bool __do_once_start(bool *done, unsigned long *flags);
-void __do_once_done(bool *done, struct static_key *once_key,
+void __do_once_done(bool *done, struct static_key_true *once_key,
unsigned long *flags);

/* Call a function exactly once. The idea of DO_ONCE() is to perform
@@ -38,8 +38,8 @@ void __do_once_done(bool *done, struct static_key *once_key,
({ \
bool ___ret = false; \
static bool ___done = false; \
- static struct static_key ___once_key = STATIC_KEY_INIT_TRUE; \
- if (static_key_true(&___once_key)) { \
+ static DEFINE_STATIC_KEY_TRUE(___once_key); \
+ if (static_branch_unlikely(&___once_key)) { \
unsigned long ___flags; \
___ret = __do_once_start(&___done, &___flags); \
if (unlikely(___ret)) { \
diff --git a/lib/once.c b/lib/once.c
index 05c8604627eb..831c5a6b0bb2 100644
--- a/lib/once.c
+++ b/lib/once.c
@@ -5,7 +5,7 @@

struct once_work {
struct work_struct work;
- struct static_key *key;
+ struct static_key_true *key;
};

static void once_deferred(struct work_struct *w)
@@ -14,11 +14,11 @@ static void once_deferred(struct work_struct *w)

work = container_of(w, struct once_work, work);
BUG_ON(!static_key_enabled(work->key));
- static_key_slow_dec(work->key);
+ static_branch_disable(work->key);
kfree(work);
}

-static void once_disable_jump(struct static_key *key)
+static void once_disable_jump(struct static_key_true *key)
{
struct once_work *w;

@@ -51,7 +51,7 @@ bool __do_once_start(bool *done, unsigned long *flags)
}
EXPORT_SYMBOL(__do_once_start);

-void __do_once_done(bool *done, struct static_key *once_key,
+void __do_once_done(bool *done, struct static_key_true *once_key,
unsigned long *flags)
__releases(once_lock)
{
--
2.14.1.480.gb18f417b89-goog

2017-08-22 18:44:45

by Hannes Frederic Sowa

Subject: Re: [PATCH] once: switch to new jump label API

Eric Biggers <[email protected]> writes:

> From: Eric Biggers <[email protected]>
>
> Switch the DO_ONCE() macro from the deprecated jump label API to the new
> one. The new one is more readable, and for DO_ONCE() it also makes the
> generated code more icache-friendly: now the one-time initialization
> code is placed out-of-line at the jump target, rather than at the inline
> fallthrough case.
>
> Signed-off-by: Eric Biggers <[email protected]>

Acked-by: Hannes Frederic Sowa <[email protected].

Thanks!

2017-09-16 04:07:59

by Eric Biggers

Subject: Re: [PATCH] once: switch to new jump label API

On Tue, Aug 22, 2017 at 02:44:41PM -0400, Hannes Frederic Sowa wrote:
> Eric Biggers <[email protected]> writes:
>
> > From: Eric Biggers <[email protected]>
> >
> > Switch the DO_ONCE() macro from the deprecated jump label API to the new
> > one. The new one is more readable, and for DO_ONCE() it also makes the
> > generated code more icache-friendly: now the one-time initialization
> > code is placed out-of-line at the jump target, rather than at the inline
> > fallthrough case.
> >
> > Signed-off-by: Eric Biggers <[email protected]>
>
> Acked-by: Hannes Frederic Sowa <[email protected].
>
> Thanks!

Great! Who though is the maintainer for this code? It seems it was originally
taken by David Miller through the networking tree. David, are you taking
further patches to the "once" functions, or should I be trying to get this into
-mm, or somewhere else?

Eric