linux-kernel - Re: [PATCH v2] ata: increase retry count but shorten duration for Calxeda controller

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Date:	Fri, 31 May 2013 08:53:37 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
CC:	Timur Tabi <timur.tabi@...xeda.com>,
	Mark Langsdorf <mark.langsdorf@...xeda.com>, tj@...nel.org,
	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [PATCH v2] ata: increase retry count but shorten duration for
 Calxeda controller

Sergei Shtylyov wrote:
> On 30-05-2013 18:26, Timur Tabi wrote:
>>> +    const unsigned long timing[] = { 5, 100, 500};
>
>> You'll save space and time if you also make this array "static",
>> otherwise the compiler will build the array every time this function is
>> called.
>
> No, *const* specifier is enough to not build this array every time. It will be put into the .const section.

gcc disagrees:

$ cat const_static.c
int f(int x) {
	const unsigned long timing[] = { 5, 100, 500};
	static const unsigned long timing2[] = { 5, 100, 500};
	return timing[x] + timing2[x];
}
$ gcc -Os -S const_static.c
$ cat const_static.s
	...
timing2.0:
        .long   5
        .long   100
        .long   500
	...
        movl    8(%ebp), %edx
        movl    $5, -16(%ebp)
        movl    $100, -12(%ebp)
        movl    $500, -8(%ebp)
        movl    timing2.0(,%edx,4), %eax
        addl    -16(%ebp,%edx,4), %eax


Regards,
Clemens
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