Subject: Re: [PATCH -v2 6/8] jump_label: Add a new static_key interface
To: Peter Zijlstra <peterz@infradead.org>, linux-kernel@vger.kernel.org,
        mingo@kernel.org
References: <20150728132055.203176565@infradead.org>
 <20150728132313.164884020@infradead.org>
Cc: 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, heiko.carstens@de.ibm.com, davem@davemloft.net
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <55B87E7A.2070509@suse.cz>
Date: Wed, 29 Jul 2015 09:19:22 +0200
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On 07/28/2015 03:21 PM, Peter Zijlstra wrote:
> +/* -------------------------------------------------------------------------- */
> +
> +/*
> + * Two type wrappers around static_key, such that we can use compile time
> + * type differentiation to emit the right code.
> + *
> + * All the below code is macros in order to play type games.
> + */
> +
> +struct static_key_true {
> +	struct static_key key;
> +};
> +
> +struct static_key_false {
> +	struct static_key key;
> +};
> +
> +#define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
> +#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }

How would one define a static key that's e.g. expected to be mostly false, but
with initial value of true, e.g. during boot?

Is the following legal? Should there be an API wrapper as well?

(struct static_key_false){ .key = STATIC_KEY_INIT_TRUE, }

Otherwise the new API seems like a big improvement, thanks :)


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