linux-kernel - Re: [tip:locking/core] locking/atomics: Simplify the op definitions in atomic.h some more

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Date:   Tue, 15 May 2018 20:11:36 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, will.deacon@....com,
        torvalds@...ux-foundation.org, paulmck@...ux.vnet.ibm.com,
        tglx@...utronix.de, hpa@...or.com,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:locking/core] locking/atomics: Simplify the op definitions
 in atomic.h some more

On Tue, May 15, 2018 at 06:53:08PM +0100, Mark Rutland wrote:
> On Tue, May 15, 2018 at 07:10:21PM +0200, Peter Zijlstra wrote:
> > On Tue, May 15, 2018 at 04:43:33PM +0100, Mark Rutland wrote:
> > > I *think* the table can encode enough info to generate atomic-long.h,
> > > atomic-instrumented.h, and the atomic.h ordering fallbacks. I'll need to
> > > flesh out the table and check that we don't end up clashing with
> > > some of the regular fallbacks.
> > 
> > Yes, details details ;-)
> > 
> > > # name	meta	args...
> > > #
> > > # Where meta contains a string of:
> > > # * B - bool: returns bool, fully ordered
> > > # * V - void: returns void, fully ordered
> > 
> > void retuns are relaxed
> 
> How about:
> 
>   V - void: returns void, no ordering variants (implicitly relaxed)

Works for me.

> > > # * I - int: returns base type, all orderings
> > > # * R - return: returns base type, all orderings
> > > # * F - fetch: returns base type, all orderings
> > > # * T - try: returns bool, all orderings
> > 
> > Little more verbose than mine, I think we can get there with X and XB
> > instead of I and T, but whatever :-)
> 
> Mhmm. I found it easier to do switch-like things this way, but it works
> regardless.

I'm a minimalist, but yeah whatever ;-)

> > > # Where args contains list of type[:name], where type is:
> > > # * v - pointer to atomic base type (atomic or atomic64)
> > > # * i - base type (int or long)
> > > # * I - pointer to base type (int or long)
> > > #
> > > add		VRF	i	v
> > > sub		VRF	i	v
> > > inc		VRF	v
> > > dec		VRF	v
> > > or		VF	i	v
> > > and		VF	i	v
> > > andnot		VF	i	v
> > > xor		VF	i	v
> > > xchg		I	v	i
> > > cmpxchg		I	v	i:old	i:new
> > > try_cmpxchg	T	v	I:old	i:new
> > > add_and_test	B	i	v
> > > sub_and_test	B	i	v
> > > dec_and_test	B	v
> > > inc_and_test	B	v

we might also want:

set		V	v	i
set_release	V	v	i
read		I	v
read_acquire	I	v

(yes, I did get the set arguments the wrong way around initially)