Re: no need to check for NULL before calling kfree() -fs/ext2/

On Tue, 29 Mar 2005, Paul Jackson wrote:

> Pekka wrote:
> >  (4) The cleanups Jesper and others are doing are to remove the
> >      _redundant_ NULL checks (i.e. it is now checked twice). 
> 
> Even such obvious changes as removing redundant checks doesn't
> seem to ensure a performance improvement.  Jesper Juhl posted
> performance data for such changes in his microbenchmark a couple
> of days ago.
> 
> As I posted then, I could swear that his numbers show:
> 
> > Just looking at the third run, it seems to me that "if (likely(p))
> > kfree(p);" beats a naked "kfree(p);" everytime, whether p is half
> > NULL's, or very few NULL's, or almost all NULL's.
> 
> Twice now I have asked Jesper to explain this strange result.
> 
I've been kept busy with other things for a while and haven't had the time 
to reply to your emails, sorry.   As I just said in another post I don't 
know how valid my numbers are, but I'll try and craft a few more tests to 
see if I can get some more solid results.

> 
> Maybe we should be following your good advice:
> 
> > You don't know that until you profile! 
> 
> instead of continuing to make these code changes.
> 
I'll gather some more numbers and post them along with any conclusions I 
believe can be drawn from them within a day or two, untill then I'll hold 
back on the patches...


-- 
Jesper Juhl


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