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DateThu, 27 Apr 2006 16:37:36 +1000
FromNick Piggin <>
SubjectRe: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
Pekka J Enberg wrote:
> On Wed, 26 Apr 2006, Kyle Moffett wrote:
> 
>>Here's code that I've found works as well as can be expected under both GCC 3
>>and GCC 4.  If xp is a known-NULL constant the whole function will be
>>optimized out completely.  If xp is known-not-NULL, then it will optimize to a
>>kfree function without the null check.  Otherwise it optimizes to call the
>>out-of-line version.
> 
> 
> Wouldn't it be better to simply remove calls to kfree() with known 
> NULL constant?

Yes, but this will optimise away the check for known non-NULL.

At the cost of icache footprint.

I think unmeasurable micro-optimisations that go against historic
CPU trends (eg. size for speed) aren't worth wasting too much
sleep over. If it is a 0.0001% speedup today, it'll be a 0.0001%
slowdown tomorrow :)

-- 
SUSE Labs, Novell Inc.
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