linux-kernel - Re: [PATCH] percpu: explain quick paths in pcpu_[de]populate

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Message-ID: <4B147918.3000503@redhat.com>
Date:	Tue, 01 Dec 2009 10:02:00 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] percpu: explain quick paths in pcpu_[de]populate_chunk()

Tejun Heo wrote:
> pcpu_[de]populate_chunk() check whether there's actually any work to
> do at the beginning and exit early if not.  This checking is done by
> seeing whether the first iteration of pcpu_for_each_[un]pop_region()
> covers the whole requested region.  The resulting code is a bit
> unusual in that it's loop-like but never loops which apparently
> confuses people.  Add comments to explain it.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Amerigo Wang <amwang@...hat.com>
> Cc: Christoph Lameter <cl@...ux-foundation.org>
> ---
> Added to percpu#for-next.  This should be clear enough, right?
> 

Nope, comments can never fix bad code.

Since these two break statements are intentional, why not use if?
Logically, the following two are equalent.

for(a1; a2; a3){
     if (a4)
        return;
     break;
}


a1;
if (a2) {
    if (a4)
        return;
}


And the latter is much more readable than the former.
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