Skip to content

Commit

Permalink
---
Browse files Browse the repository at this point in the history
yaml
---
r: 17025
b: refs/heads/master
c: a771f2b
h: refs/heads/master
i:
  17023: 4535d02
v: v3
  • Loading branch information
Arjan van de Ven authored and Linus Torvalds committed Jan 9, 2006
1 parent 5ef3384 commit a9d6c48
Show file tree
Hide file tree
Showing 2 changed files with 32 additions and 4 deletions.
2 changes: 1 addition & 1 deletion [refs]
Original file line number Diff line number Diff line change
@@ -1,2 +1,2 @@
---
refs/heads/master: e0804b17984afa1504649e2535db489d2a3029b6
refs/heads/master: a771f2b82aa266fe578468deed82f797e26a3dc4
34 changes: 31 additions & 3 deletions trunk/Documentation/CodingStyle
Original file line number Diff line number Diff line change
Expand Up @@ -344,7 +344,7 @@ Remember: if another thread can find your data structure, and you don't
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.

Expand Down Expand Up @@ -429,7 +429,35 @@ from void pointer to any other pointer type is guaranteed by the C programming
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.
Expand All @@ -453,4 +481,4 @@ Kernel CodingStyle, by greg@kroah.com at OLS 2002:
http://www.kroah.com/linux/talks/ols_2002_kernel_codingstyle_talk/html/

--
Last updated on 16 February 2004 by a community effort on LKML.
Last updated on 30 December 2005 by a community effort on LKML.

0 comments on commit a9d6c48

Please sign in to comment.