Date: Wed, 29 Jul 2015 08:43:22 +0200
From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jasonbaron0@gmail.com,
        bp@alien8.de, luto@amacapital.net, tglx@linutronix.de,
        rostedt@goodmis.org, will.deacon@arm.com, liuj97@gmail.com,
        rabin@rab.in, ralf@linux-mips.org, ddaney@caviumnetworks.com,
        benh@kernel.crashing.org, michael@ellerman.id.au, davem@davemloft.net,
        vbabka@suse.cz
Subject: Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface
Message-ID: <20150729064322.GA3953@osiris>
References: <20150728132055.203176565@infradead.org>
 <20150728132313.164884020@infradead.org>
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On Tue, Jul 28, 2015 at 03:21:01PM +0200, Peter Zijlstra 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@infradead.org>
> ---
>  arch/arm/include/asm/jump_label.h     |   24 +++--
>  arch/arm64/include/asm/jump_label.h   |   18 +++-
>  arch/mips/include/asm/jump_label.h    |   19 ++++
>  arch/powerpc/include/asm/jump_label.h |   19 ++++
>  arch/s390/include/asm/jump_label.h    |   19 ++++
>  arch/sparc/include/asm/jump_label.h   |   35 ++++++--
>  arch/x86/include/asm/jump_label.h     |   21 ++++
>  include/linux/jump_label.h            |  143 ++++++++++++++++++++++++++++++++--
>  kernel/jump_label.c                   |   35 ++++++--
>  9 files changed, 294 insertions(+), 39 deletions(-)

for the s390 part:

Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>

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