linux-kernel - Re: [PATCH v2] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg

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Message-ID: <20160316080437.GA31133@gmail.com>
Date:	Wed, 16 Mar 2016 09:04:37 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.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 v2] atomic: Fix bugs in 'fetch_or()' and rename it to
 'xchg_or()'


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Mar 15, 2016 at 01:21:45PM +0100, Ingo Molnar wrote:
> >  - Renaming fetch_or() to xchg_or(), recognizing that the semantics
> >    are xchg()-alike.
> 
> Let me add another argument for why I don't like the "exchange/swap
> (and) add" naming.
> 
> Exchange (and swap) replace one value for another, like:
> 
> 	old = xchg(ptr, val);
> 
> Whatever was there, gets replaced by the independent value in @val.
> Straight up replacement.
> 
> However with something like xchg_or, you don't do a direct replacement
> with an unrelated value. Instead you modify the pre-existing value. So
> there really isn't an exchange at all.
> 
> So "fetch (and) or" really describes the operation better. You load
> (fetch) the value and then modify it, in an indivisible (aka atomic)
> fashion.

Ok!

Could we at least somehow sneak the notion of 'atomicity' into it?

	fetch_or()
	fetch_and()
	fetch_not()

vs.

	fetch_atomic_or()
	fetch_atomic_and()
	fetch_atomic_not()

vs.

	atomic_fetch_or()
	atomic_fetch_and()
	atomic_fetch_not()

?

Thanks,

	Ingo