linux-kernel - Re: Kernel broken on processors without performance counters

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Message-ID: <20150723145801.GI25159@twins.programming.kicks-ass.net>
Date:	Thu, 23 Jul 2015 16:58:01 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Baron <jasonbaron0@...il.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Kees Cook <keescook@...omium.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Vince Weaver <vince@...ter.net>,
	"hillf.zj" <hillf.zj@...baba-inc.com>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: Kernel broken on processors without performance counters

On Thu, Jul 23, 2015 at 10:19:52AM -0400, Jason Baron wrote:
> >
> > #define static_branch_likely(x)							\
> > ({										\
> > 	bool branch;								\
> > 	if (__builtin_types_compatible_p(typeof(x), struct static_key_true))	\
> > 		branch = !arch_static_branch(&(x)->key, false);			\
> > 	else if (__builtin_types_compatible_p(typeof(x), struct static_key_false)) \
> > 		branch = !arch_static_branch_jump(&(x)->key, true);		\
> > 	else									\
> > 		branch = ____wrong_branch_error();				\
> > 	branch;									\
> > })
> >
> > #define static_branch_unlikely(x)						\
> > ({										\
> > 	bool branch;								\
> > 	if (__builtin_types_compatible_p(typeof(x), struct static_key_true))	\
> > 		branch = arch_static_branch(&(x)->key, true);			\
> > 	else if (__builtin_types_compatible_p(typeof(x), struct static_key_false)) \
> > 		branch = arch_static_branch_jump(&(x)->key, false);		\
> > 	else									\
> > 		branch = ____wrong_branch_error();				\
> > 	branch;									\
> > })
> >
> 
> In 'static_branch_unlikely()', I think  arch_static_branch() and
> arch_static_branch_jump() are reversed.

Yes, you're right. But I think I need a nap before touching this stuff
again :-)

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