On 27/11/2014 13:25, David Laight wrote:
From: Joe Perches
On Wed, 2014-11-26 at 10:34 -0800, Alexei Starovoitov wrote:
On Wed, Nov 26, 2014 at 10:02 AM, Joe Perches <j...@perches.com> wrote:
On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote:
On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches <j...@perches.com> wrote:
Is there any value in reordering these tests for frequency
or maybe using | instead of || to avoid multiple jumps?
probably not. It's not a critical path.
compiler may fuse conditions depending on values anyway.
If it was a critical path, we could have used
(1 << reg) & mask trick.
I picked explicit 'return true' else 'return false' here,
because it felt easier to read. Just a matter of taste.
There is a size difference though: (allyesconfig)
$ size arch/x86/net/built-in.o*
text data bss dec hex filename
12999 1012 4336 18347 47ab arch/x86/net/built-in.o.new
13177 1076 4592 18845 499d arch/x86/net/built-in.o.old
interesting. Compiler obviously thinks that 178 byte increase
with -O2 is the right trade off. Which I agree with :)
If I think dropping 'inline' and using -Os will give bigger savings...
This was allyesconfig which already uses -Os
Using -O2, there is no difference using inline
or not, but the size delta with the bitmask is
much larger
$ size arch/x86/net/built-in.o* (allyesconfig, but not -Os)
text data bss dec hex filename
13410 820 3624 17854 45be arch/x86/net/built-in.o.new
16130 884 4200 21214 52de arch/x86/net/built-in.o.old
16130 884 4200 21214 52de arch/x86/net/built-in.o.static
That is quite a big % change in the code size.
Why the change in data?
David
Do you want me to propose a second version, or should I just
drop it all together ?
I am a new contributor so I have no experience in that sort of thing.
Quentin
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