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Message-ID: <CAMuHMdXG4veEOqr5vcZQEQH55=CT6CPXOfqrc_m=fpXEseAdLA@mail.gmail.com>
Date: Thu, 16 Jun 2016 12:08:27 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Will Deacon <will.deacon@....com>,
Paul McKenney <paulmck@...ux.vnet.ibm.com>,
boqun.feng@...il.com, waiman.long@....com,
Frédéric Weisbecker <fweisbec@...il.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Linux-Arch <linux-arch@...r.kernel.org>,
Richard Henderson <rth@...ddle.net>,
Vineet Gupta <vgupta@...opsys.com>,
Russell King <linux@....linux.org.uk>,
Hans-Christian Noren Egtvedt <egtvedt@...fundet.no>,
Miao Steven <realmz6@...il.com>,
Yoshinori Sato <ysato@...rs.sourceforge.jp>,
Richard Kuo <rkuo@...eaurora.org>,
Tony Luck <tony.luck@...el.com>,
James Hogan <james.hogan@...tec.com>,
Ralf Baechle <ralf@...ux-mips.org>,
David Howells <dhowells@...hat.com>,
"James E.J. Bottomley" <jejb@...isc-linux.org>,
Michael Ellerman <mpe@...erman.id.au>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Rich Felker <dalias@...c.org>,
"David S. Miller" <davem@...emloft.net>, cmetcalf@...lanox.com,
Max Filippov <jcmvbkbc@...il.com>,
Arnd Bergmann <arnd@...db.de>, dbueso@...e.de,
Wu Fengguang <fengguang.wu@...el.com>,
linux-m68k <linux-m68k@...ts.linux-m68k.org>
Subject: Re: [PATCH -v2 14/33] locking,m68k: Implement atomic_fetch_{add,sub,and,or,xor}()
Hi Peter,
On Tue, May 31, 2016 at 12:19 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> Implement FETCH-OP atomic primitives, these are very similar to the
> existing OP-RETURN primitives we already have, except they return the
> value of the atomic variable _before_ modification.
>
> This is especially useful for irreversible operations -- such as
> bitops (because it becomes impossible to reconstruct the state prior
> to modification).
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> arch/m68k/include/asm/atomic.h | 53 +++++++++++++++++++++++++++++++++++++----
> 1 file changed, 49 insertions(+), 4 deletions(-)
>
> --- a/arch/m68k/include/asm/atomic.h
> +++ b/arch/m68k/include/asm/atomic.h
> @@ -38,6 +38,13 @@ static inline void atomic_##op(int i, at
>
> #ifdef CONFIG_RMW_INSNS
>
> +/*
> + * Am I reading these CAS loops right in that %2 is the old value and the first
> + * iteration uses an uninitialized value?
> + *
> + * Would it not make sense to add: tmp = atomic_read(v); to avoid this?
> + */
> +
> #define ATOMIC_OP_RETURN(op, c_op, asm_op) \
> static inline int atomic_##op##_return(int i, atomic_t *v) \
> { \
Do we want the above comment in the code?
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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