some questions about kernel source

[John Mahoney]

On Thu, Feb 17, 2011 at 9:17 AM, loody <miloody at gmail.com> wrote:
> hi :-)
>
> 2011/2/16 Mulyadi Santosa <mulyadi.santosa at gmail.com>:
>> Hi :)
>>
>> On Wed, Feb 16, 2011 at 12:59, Rajat Jain <rajatjain at juniper.net> wrote:
>>> Hello loody,
>>>
>>>> 1. in kernel/trace, I always see "__read_mostly" at the end of
>>>> parameter is that a compiler optimization parameter?
>>>
>>> Yes, it is a hint to the compiler that the parameter is mostly read, thus if the compiler has to make a decision between optimizing one of the read / write paths, it will optimize the read path even at the expense of write path.
>>
>>
>> To be precise, they will be grouped into same cache line as much as
>> possible. By doing so, those cache line won't be invalidated so often
>> (keeping them "hot" :) hehehhe )
>
> I cannot find it on the gcc manual.
> is it a option in kernel for kernel usage?
> if so, where I can found them.
> If not, can I use it on normal user level program?
>

It is a macro defined for x86 as:

#define __read_mostly __attribute__((__section__(".data..read_mostly")))

http://lxr.linux.no/linux+v2.6.37/arch/x86/include/asm/cache.h

---snip---
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--
John