[PATCH] Add a section about inlining to Documentation/CodingStyle

have a reference count on it, you almost certainly have a bug.

		Chapter 11: Macros, Enums, Inline functions and RTL

		Chapter 11: Macros, Enums and RTL

Names of macros defining constants and labels in enums are capitalized.

language.

		Chapter 14: References

		Chapter 14: The inline disease

There appears to be a common misperception that gcc has a magic "make me

faster" speedup option called "inline". While the use of inlines can be

appropriate (for example as a means of replacing macros, see Chapter 11), it

very often is not. Abundant use of the inline keyword leads to a much bigger

kernel, which in turn slows the system as a whole down, due to a bigger

icache footprint for the CPU and simply because there is less memory

available for the pagecache. Just think about it; a pagecache miss causes a

disk seek, which easily takes 5 miliseconds. There are a LOT of cpu cycles

that can go into these 5 miliseconds.

A reasonable rule of thumb is to not put inline at functions that have more

than 3 lines of code in them. An exception to this rule are the cases where

a parameter is known to be a compiletime constant, and as a result of this

constantness you *know* the compiler will be able to optimize most of your

function away at compile time. For a good example of this later case, see

the kmalloc() inline function.

Often people argue that adding inline to functions that are static and used

only once is always a win since there is no space tradeoff. While this is

technically correct, gcc is capable of inlining these automatically without

help, and the maintenance issue of removing the inline when a second user

appears outweighs the potential value of the hint that tells gcc to do

something it would have done anyway.

		Chapter 15: References

The C Programming Language, Second Edition

by Brian W. Kernighan and Dennis M. Ritchie.

http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/

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Last updated on 16 February 2004 by a community effort on LKML.

Last updated on 30 December 2005 by a community effort on LKML.