linux-kernel - Re: [RFC][PATCH]: documentation,atomic: Add a new atomic

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Message-ID: <20170712130826.6qs4fcrwkowe4uoh@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Jul 2017 15:08:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Will Deacon <will.deacon@....com>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][PATCH]: documentation,atomic: Add a new atomic_t document

On Wed, Jul 12, 2017 at 08:53:47PM +0800, Boqun Feng wrote:
> On Mon, Jun 12, 2017 at 04:49:29PM +0200, Peter Zijlstra wrote:
> [...]
> > -Any atomic operation that modifies some state in memory and returns information
> > -about the state (old or new) implies an SMP-conditional general memory barrier
> > -(smp_mb()) on each side of the actual operation (with the exception of
> > -explicit lock operations, described later).  These include:
> > -
> > -	xchg();
> > -	atomic_xchg();			atomic_long_xchg();
> > -	atomic_inc_return();		atomic_long_inc_return();
> > -	atomic_dec_return();		atomic_long_dec_return();
> > -	atomic_add_return();		atomic_long_add_return();
> > -	atomic_sub_return();		atomic_long_sub_return();
> > -	atomic_inc_and_test();		atomic_long_inc_and_test();
> > -	atomic_dec_and_test();		atomic_long_dec_and_test();
> > -	atomic_sub_and_test();		atomic_long_sub_and_test();
> > -	atomic_add_negative();		atomic_long_add_negative();
> > -	test_and_set_bit();
> > -	test_and_clear_bit();
> > -	test_and_change_bit();
> > -
> 
> The bit related operations are removed from memory-barriers.txt, I think
> we'd better add them in atomic_t.txt? By "them", I mean:
> 
> 	test_and_{set,clear,change}_bit() as RMW atomic
> 
> 	{set,clear,change}_bit() as non-RMW atomic
> 
> 	test_and_set_bit_lock()
> 	clear_bit_unlock() as non-RMW(but barrier-like) atomic

I was thinking maybe a separate file, as I was hoping to eventually
write a separate file on spinlocks too.

I'd like to keep the the new thing purely about the atomic* family of
stuff, that's large enough as is.