linux-kernel - Re: [patch] add optimized generic percpu accessors

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Date:	Thu, 15 Jan 2009 14:59:35 +0100
From:	"roel kluin" <roel.kluin@...il.com>
To:	"Tejun Heo" <tj@...nel.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"Brian Gerst" <brgerst@...il.com>, ebiederm@...ssion.com,
	cl@...ux-foundation.org, rusty@...tcorp.com.au, travis@....com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	steiner@....com, hugh@...itas.com
Subject: Re: [patch] add optimized generic percpu accessors

> +#ifndef percpu_read
> +# define percpu_read(var)                                              \
> +  ({                                                                   \
> +       typeof(per_cpu_var(var)) __tmp_var__;                           \
> +       __tmp_var__ = get_cpu_var(var);                                 \
> +       put_cpu_var(var);                                               \
> +       __tmp_var__;                                                    \
> +  })
> +#endif

I'm sorry for your eyes, but since var occurs twice, isn't it better to do:

# define percpu_read(var)                                              \
  ({                                                                   \
       typeof(var) __pcpu_read_var__ = var;
               \
       typeof(per_cpu_var(__pcpu_read_var__)) __tmp_var__;                    \
       __tmp_var__ = get_cpu_var(__pcpu_read_var__);                           \
       put_cpu_var(__pcpu_read_var__);                                         \
       __tmp_var__;                                                    \
  })

> +
> +#define __percpu_generic_to_op(var, val, op)                           \
> +do {                                                                   \
> +       get_cpu_var(var) op val;                                        \
> +       put_cpu_var(var);                                               \
> +} while (0)

and:

#define __percpu_generic_to_op(var, val, op)                           \
do {                                                                   \
       typeof(var) __pcpu_gto_var__ = var;
              \
       get_cpu_var(__pcpu_gto_var__) op val;
             \
       put_cpu_var(__pcpu_gto_var__);
             \
} while (0)
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