regarding synchronization code

regarding synchronization code

[Sri Ram Vemulpali]

Hi all,

  I am encountering alot macros in the code. I did not understand what
those macro means.

  Can anyone explain them and the use of them putting them like that.

   "unlikely"
   "always_inline"  -- defined at the signature of the function.
   "inline" -- I know inline keyword in compiler is used to place the
code in to the caller function at the time of compiler, but why
declared as macro

    Any help would be appreciated.

-- 
Regards,
Sri.

Re: regarding synchronization code

[Gregory Haskins]

>>> On 9/24/2010 at 06:56 PM, in message
<AANLkTikhWVuL18zRcPTu2TcEQrv8Bpr4O0eafNsPgNjt@mail.gmail.com>, Sri Ram
Vemulpali <sri.ram.gmu06@gmail.com> wrote: 
> Hi all,
> 
>   I am encountering alot macros in the code. I did not understand what
> those macro means.
> 
>   Can anyone explain them and the use of them putting them like that.
> 
>    "unlikely"

Related to gcc branch-prediction, iirc.

>    "always_inline"  -- defined at the signature of the function.
>    "inline" -- I know inline keyword in compiler is used to place the
> code in to the caller function at the time of compiler, but why
> declared as macro

Probably so it can be enabled/disabled as a .config option.

Kind Regards,
-Greg

Re: regarding synchronization code

[Dave Hylands]

Hi Sri,

On Fri, Sep 24, 2010 at 3:56 PM, Sri Ram Vemulpali wrote:
> Hi all,
>
>  I am encountering alot macros in the code. I did not understand what
> those macro means.
>
>  Can anyone explain them and the use of them putting them like that.
>
>   "unlikely"

This has to do with branch prediction. If the architecture that you're
building for supports branch prediction then this provides a hint to
say that the following test is unlikely to pass, so the branch
prediction will be setup to take the likely path.

>   "always_inline"  -- defined at the signature of the function.

Exactly what it says - always make the function an inline function.
The inline keyword is normally just a hint or suggestion to the
compiler, whereas the always_inline says that the function should
always be inlined, even if optimizations to perform function inlining
is disabled.
<http://gcc.gnu.org/onlinedocs/gcc-4.0.4/gcc/Function-Attributes.html>

>   "inline" -- I know inline keyword in compiler is used to place the
> code in to the caller function at the time of compiler, but why
> declared as macro

There are some CONFIG options which allow inline behaviour to be tweaked:
<http://cateee.net/lkddb/web-lkddb/OPTIMIZE_INLINING.html>

-- 
Dave Hylands
Shuswap, BC, Canada
http://www.DaveHylands.com/
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Re: regarding synchronization code

[Michael Blizek]

Hi!

On 18:56 Fri 24 Sep     , Sri Ram Vemulpali wrote:
> Hi all,
> 
>   I am encountering alot macros in the code. I did not understand what
> those macro means.
> 
>   Can anyone explain them and the use of them putting them like that.
> 
>    "unlikely"

likely() and unlikely() are wrappers around gcc extensions to give hints about
whether a given branch will likely be taken or not. When done correctly, this
can improve performance.

>    "always_inline"  -- defined at the signature of the function.

This can be used because "inline" is not always inlined. There should be a gcc
option which causes all inline code to be not inlined.

>    "inline" -- I know inline keyword in compiler is used to place the
> code in to the caller function at the time of compiler, but why
> declared as macro

Where do you see inline declared as a macro?

	-Michi
-- 
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.twilightparadox.com


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Re: regarding synchronization code

[Sri Ram Vemulpali]

I am just saying I know inline keyword. But what is always_inline.

Thanks for replies and explanations. I got it now.

Regards,
Sri.

On Sat, Sep 25, 2010 at 4:48 AM, Michael Blizek
<michi1@michaelblizek.twilightparadox.com> wrote:
> Hi!
>
> On 18:56 Fri 24 Sep     , Sri Ram Vemulpali wrote:
>> Hi all,
>>
>>   I am encountering alot macros in the code. I did not understand what
>> those macro means.
>>
>>   Can anyone explain them and the use of them putting them like that.
>>
>>    "unlikely"
>
> likely() and unlikely() are wrappers around gcc extensions to give hints about
> whether a given branch will likely be taken or not. When done correctly, this
> can improve performance.
>
>>    "always_inline"  -- defined at the signature of the function.
>
> This can be used because "inline" is not always inlined. There should be a gcc
> option which causes all inline code to be not inlined.
>
>>    "inline" -- I know inline keyword in compiler is used to place the
>> code in to the caller function at the time of compiler, but why
>> declared as macro
>
> Where do you see inline declared as a macro?
>
>        -Michi
> --
> programing a layer 3+4 network protocol for mesh networks
> see http://michaelblizek.twilightparadox.com
>
>



-- 
Regards,
Sri.
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Re: regarding synchronization code

[Bond]

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On Sat, Sep 25, 2010 at 10:34 PM, Sri Ram Vemulpali <sri.ram.gmu06@gmail.com
> wrote:

> I am just saying I know inline keyword. But what is always_inline.
>

I wonder why you were not given any lecture to Google etc as I get in my
other threads.

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