linux-kernel - Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg

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Date:	Tue, 15 Mar 2016 13:42:44 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to
 'xchg_or()'

On Tue, Mar 15, 2016 at 01:08:35PM +0100, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, Mar 15, 2016 at 10:32:45AM +0100, Ingo Molnar wrote:
> > >  2) its naming sucks. "fetch_or()" does not really signal that it's a
> > >     fundamentally atomic operation, nor what API family it belongs to.
> > 
> > I disagree there, the fetch-$op naming is widely used for atomic
> > operations that return the previous value. See for example the C/C++11
> > atomic ops.
> 
> The problem I see is that we don't really have the fetch_*() naming in the kernel 
> right now, while we do have the xchg_*() naming. The latter is 'obviously' an 
> atomic operation - while 'fetch' could be anything.

We don't have xchg_*() naming, we have xchg() and that's about it. And
yes, people know xchg() is an atomic op. But 'fetch (and) or' is also
atomic, it has to be, it needs to do 2 operations in 1.

Furthermore, the relevant wikipedia page is:

  https://en.wikipedia.org/wiki/Fetch-and-add

So the naming is widely established.