Re: [PATCH 2/4] arch: Clean up asm/barrier.h implementations using asm-generic/barrier.h

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

* peterz@infradead.org (peterz@infradead.org) wrote:
> We're going to be adding a few new barrier primitives, and in order to
> avoid endless duplication make more agressive use of
> asm-generic/barrier.h.
> 
> Change the asm-generic/barrier.h such that it allows partial barrier
> definitions and fills out the rest with defaults.
> 
> There are a few architectures (h8300, m32r, m68k) that could probably
> do away with their barrier.h file entirely but are kept for now due to
> their unconventional nop() implementation.

FWIW, we're using a very similar scheme for our memory barrier
implementation in Userspace RCU. We include a generic header at the end,
and we have per-architecture macro override, with ifdefs to see if we
need to use the generic version.

Comments below,

> 
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> Cc: Michael Ellerman <michael@ellerman.id.au>
> Cc: Michael Neuling <mikey@neuling.org>
> Cc: Russell King <linux@arm.linux.org.uk>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> Cc: Victor Kaplansky <VICTORK@il.ibm.com>
> Suggested-by: Geert Uytterhoeven <geert@linux-m68k.org>
> Reviewed-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> ---
>  arch/alpha/include/asm/barrier.h      |   25 ++--------
>  arch/arc/include/asm/Kbuild           |    1 
>  arch/arc/include/asm/atomic.h         |    5 ++
>  arch/arc/include/asm/barrier.h        |   42 -----------------
>  arch/avr32/include/asm/barrier.h      |   17 ++-----
>  arch/blackfin/include/asm/barrier.h   |   18 -------
>  arch/cris/include/asm/Kbuild          |    1 
>  arch/cris/include/asm/barrier.h       |   25 ----------
>  arch/frv/include/asm/barrier.h        |    8 ---
>  arch/h8300/include/asm/barrier.h      |   21 --------
>  arch/hexagon/include/asm/Kbuild       |    1 
>  arch/hexagon/include/asm/barrier.h    |   41 -----------------
>  arch/m32r/include/asm/barrier.h       |   80 ----------------------------------
>  arch/m68k/include/asm/barrier.h       |   14 -----
>  arch/microblaze/include/asm/Kbuild    |    1 
>  arch/microblaze/include/asm/barrier.h |   27 -----------
>  arch/mn10300/include/asm/Kbuild       |    1 
>  arch/mn10300/include/asm/barrier.h    |   37 ---------------
>  arch/parisc/include/asm/Kbuild        |    1 
>  arch/parisc/include/asm/barrier.h     |   35 --------------
>  arch/score/include/asm/Kbuild         |    1 
>  arch/score/include/asm/barrier.h      |   16 ------
>  arch/sh/include/asm/barrier.h         |   21 +-------
>  arch/sparc/include/asm/barrier_32.h   |   11 ----
>  arch/tile/include/asm/barrier.h       |   68 ----------------------------
>  arch/unicore32/include/asm/barrier.h  |   11 ----
>  arch/xtensa/include/asm/barrier.h     |    9 ---
>  include/asm-generic/barrier.h         |   44 ++++++++++++------
>  28 files changed, 64 insertions(+), 518 deletions(-)
> 
[...]

> Index: linux-2.6/arch/arc/include/asm/atomic.h
> ===================================================================
> --- linux-2.6.orig/arch/arc/include/asm/atomic.h	2013-11-07 17:03:11.626900787 +0100
> +++ linux-2.6/arch/arc/include/asm/atomic.h	2013-11-07 17:03:11.607900434 +0100
> @@ -190,6 +190,11 @@
>  
>  #endif /* !CONFIG_ARC_HAS_LLSC */
>  
> +#define smp_mb__before_atomic_dec()	barrier()
> +#define smp_mb__after_atomic_dec()	barrier()
> +#define smp_mb__before_atomic_inc()	barrier()
> +#define smp_mb__after_atomic_inc()	barrier()

Maybe split the before/after atomic inc/dec change to a separate patch ?

> +
>  /**
>   * __atomic_add_unless - add unless the number is a given value
>   * @v: pointer of type atomic_t
> Index: linux-2.6/arch/arc/include/asm/barrier.h
> ===================================================================
> --- linux-2.6.orig/arch/arc/include/asm/barrier.h	2013-11-07 17:03:11.626900787 +0100
> +++ /dev/null	1970-01-01 00:00:00.000000000 +0000
> @@ -1,42 +0,0 @@
> -/*
> - * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
> - *
> - * This program is free software; you can redistribute it and/or modify
> - * it under the terms of the GNU General Public License version 2 as
> - * published by the Free Software Foundation.
> - */
> -
> -#ifndef __ASM_BARRIER_H
> -#define __ASM_BARRIER_H
> -
> -#ifndef __ASSEMBLY__
> -
> -/* TODO-vineetg: Need to see what this does, don't we need sync anywhere */
> -#define mb() __asm__ __volatile__ ("" : : : "memory")
> -#define rmb() mb()
> -#define wmb() mb()
> -#define set_mb(var, value)  do { var = value; mb(); } while (0)
> -#define set_wmb(var, value) do { var = value; wmb(); } while (0)
> -#define read_barrier_depends()  mb()
> -
> -/* TODO-vineetg verify the correctness of macros here */
> -#ifdef CONFIG_SMP
> -#define smp_mb()        mb()
> -#define smp_rmb()       rmb()
> -#define smp_wmb()       wmb()
> -#else
> -#define smp_mb()        barrier()
> -#define smp_rmb()       barrier()
> -#define smp_wmb()       barrier()
> -#endif
> -
> -#define smp_mb__before_atomic_dec()	barrier()
> -#define smp_mb__after_atomic_dec()	barrier()
> -#define smp_mb__before_atomic_inc()	barrier()
> -#define smp_mb__after_atomic_inc()	barrier()
> -
> -#define smp_read_barrier_depends()      do { } while (0)
> -
> -#endif
> -
> -#endif

[...]

> Index: linux-2.6/arch/hexagon/include/asm/barrier.h
> ===================================================================
> --- linux-2.6.orig/arch/hexagon/include/asm/barrier.h	2013-11-07 17:03:11.626900787 +0100
> +++ /dev/null	1970-01-01 00:00:00.000000000 +0000
> @@ -1,41 +0,0 @@
> -/*
> - * Memory barrier definitions for the Hexagon architecture
> - *
> - * Copyright (c) 2010-2011, The Linux Foundation. All rights reserved.
> - *
> - * This program is free software; you can redistribute it and/or modify
> - * it under the terms of the GNU General Public License version 2 and
> - * only version 2 as published by the Free Software Foundation.
> - *
> - * This program is distributed in the hope that it will be useful,
> - * but WITHOUT ANY WARRANTY; without even the implied warranty of
> - * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> - * GNU General Public License for more details.
> - *
> - * You should have received a copy of the GNU General Public License
> - * along with this program; if not, write to the Free Software
> - * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
> - * 02110-1301, USA.
> - */
> -
> -#ifndef _ASM_BARRIER_H
> -#define _ASM_BARRIER_H
> -
> -#define rmb()				barrier()
> -#define read_barrier_depends()		barrier()
> -#define wmb()				barrier()
> -#define mb()				barrier()
> -#define smp_rmb()			barrier()
> -#define smp_read_barrier_depends()	barrier()
> -#define smp_wmb()			barrier()
> -#define smp_mb()			barrier()
> -#define smp_mb__before_atomic_dec()	barrier()
> -#define smp_mb__after_atomic_dec()	barrier()
> -#define smp_mb__before_atomic_inc()	barrier()
> -#define smp_mb__after_atomic_inc()	barrier()

This seems to remove before/after atomic inc/dec for hexagon, but I
don't see where they are added back ?

> -
> -/*  Set a value and use a memory barrier.  Used by the scheduler somewhere.  */
> -#define set_mb(var, value) \
> -	do { var = value; mb(); } while (0)
> -
> -#endif /* _ASM_BARRIER_H */

[...]

> Index: linux-2.6/include/asm-generic/barrier.h
> ===================================================================
> --- linux-2.6.orig/include/asm-generic/barrier.h	2013-11-07 17:03:11.626900787 +0100
> +++ linux-2.6/include/asm-generic/barrier.h	2013-11-07 17:03:11.623900731 +0100
> @@ -1,4 +1,5 @@
> -/* Generic barrier definitions, based on MN10300 definitions.
> +/*
> + * Generic barrier definitions, originally based on MN10300 definitions.
>   *
>   * It should be possible to use these on really simple architectures,
>   * but it serves more as a starting point for new ports.
> @@ -16,35 +17,50 @@
>  
>  #ifndef __ASSEMBLY__
>  
> -#define nop() asm volatile ("nop")
> +#include <linux/compiler.h>
> +
> +#ifndef nop
> +#define nop()	asm volatile ("nop")
> +#endif
>  

I don't really understand why "no-op" sits within barrier.h. It might be
a lack of imagination on my part though.

Other than that

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com