Re: [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 :)

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---

• References:
  • [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Hua Zhong <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: "Pekka Enberg" <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Arjan van de Ven <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Pekka J Enberg <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Arjan van de Ven <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Jörn Engel <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Arjan van de Ven <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Pekka J Enberg <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Arjan van de Ven <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Jörn Engel <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Bart Hartgers <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Bart Hartgers <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Kyle Moffett <[email protected]>
  • Re: [PATCH] likely cleanup: remove unlikely for kfree(NULL)
    • From: Pekka J Enberg <[email protected]>

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