linux-kernel - Re: [PATCH -v2 6/8] jump_label: Add a new static

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Message-Id: <23C8FA53-2D16-4A77-BC2A-98CE32AE317C@gmail.com>
Date:	Tue, 4 Aug 2015 14:50:32 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	jasonbaron0@...il.com, bp@...en8.de, luto@...capital.net,
	tglx@...utronix.de, rostedt@...dmis.org, will.deacon@....com,
	liuj97@...il.com, rabin@....in, ralf@...ux-mips.org,
	ddaney@...iumnetworks.com, benh@...nel.crashing.org,
	michael@...erman.id.au, heiko.carstens@...ibm.com,
	davem@...emloft.net, vbabka@...e.cz
Subject: Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface


> On Jul 28, 2015, at 21:21, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> There are various problems and short-comings with the current
> static_key interface:
> 
> - static_key_{true,false}() read like a branch depending on the key
>   value, instead of the actual likely/unlikely branch depending on
>   init value.
> 
> - static_key_{true,false}() are, as stated above, tied to the
>   static_key init values STATIC_KEY_INIT_{TRUE,FALSE}.
> 
> - we're limited to the 2 (out of 4) possible options that compile to
>   a default NOP because that's what our arch_static_branch() assembly
>   emits.
> 
> So provide a new static_key interface:
> 
>  DEFINE_STATIC_KEY_TRUE(name);
>  DEFINE_STATIC_KEY_FALSE(name);
> 
> Which define a key of different types with an initial true/false
> value.
> 
> Then allow:
> 
>   static_branch_likely()
>   static_branch_unlikely()
> 
> to take a key of either type and emit the right instruction for the
> case.
> 
> This means adding a second arch_static_branch_jump() assembly helper
> which emits a JMP per default.
> 
> In order to determine the right instruction for the right state,
> encode the branch type in the LSB of jump_entry::key.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> 
is this means static_key_{true,false}() are deprecated ?
do you need mark static_key_{true,false}() as deprecated?
like this:
static __always_inline  __deprecated bool static_key_false(struct static_key *key)  ?
Thanks


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