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Subject: Re: [PATCH v4 14/18] static_call: Add static_cond_call()
To:     Peter Zijlstra <peterz@infradead.org>, x86@kernel.org
Cc:     linux-kernel@vger.kernel.org, rostedt@goodmis.org,
        mhiramat@kernel.org, bristot@redhat.com, jbaron@akamai.com,
        torvalds@linux-foundation.org, tglx@linutronix.de,
        mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org,
        ard.biesheuvel@linaro.org, jpoimboe@redhat.com,
        pbonzini@redhat.com, mathieu.desnoyers@efficios.com
References: <20200501202849.647891881@infradead.org>
 <20200501202944.593400184@infradead.org>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <1238787e-d97d-f09b-d76d-2df2dc273f4b@rasmusvillemoes.dk>
Date:   Sat, 2 May 2020 15:08:00 +0200
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On 01/05/2020 22.29, Peter Zijlstra wrote:
> Extend the static_call infrastructure to optimize the following common
> pattern:
> 
> 	if (func_ptr)
> 		func_ptr(args...)
> 
> +
>  #define static_call(name)	__static_call(name)
> +#define static_cond_call(name)	(void)__static_call(name)
>  
> +
>  #define static_call(name)	__static_call(name)
> +#define static_cond_call(name)	(void)__static_call(name)
>  

> +#define static_cond_call(name)						\
> +	if (STATIC_CALL_KEY(name).func)					\
> +		((typeof(STATIC_CALL_TRAMP(name))*)(STATIC_CALL_KEY(name).func))
> +

This addresses neither the READ_ONCE issue nor the fact that, AFAICT,
the semantics of

  static_cond_call(foo)(i++)

will depend on CONFIG_HAVE_STATIC_CALL. Also, I'd have appreciated being
cc'ed on new revisions instead of stumbling on it by chance.

Rasmus