[ltt-dev] [PATCH RFC] Native ARM7L support

[Mathieu Desnoyers]

* Paul E. McKenney (paulmck at linux.vnet.ibm.com) wrote:
> The machine I am using is cortex-a9.  It may be necessary to create a
> more intelligent mapping to the many variants of ARM.  Interestingly
> enough, __sync_synchronize() -still- fails, so use an explicit asm
> for the dmb instruction.
> 
> Leaving off the '-O' gives freaking slow results.  ;-)

Is this -O problem something we should fix at an higher level ? (e.g. for all
arch ?)

More comments below,

> 
> Signed-off-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> ---
> 
>  configure.ac               |    4 +++
>  urcu/arch_armv7l.h         |   59 +++++++++++++++++++++++++++++++++++++++++++++
>  urcu/uatomic_arch_armv7l.h |   48 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 111 insertions(+)
> 
> diff --git a/configure.ac b/configure.ac
> index 9274337..9e2615f 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -51,6 +51,7 @@ case $host_cpu in
>  	s390x) ARCHTYPE="s390" ;;
>  	sparc64) ARCHTYPE="sparc64" ;;
>  	alpha*) ARCHTYPE="alpha" ;;
> +	armv7l) ARCHTYPE="armv7l" ;;
>  	*) ARCHTYPE="unknown";;
>  esac
>  
> @@ -61,6 +62,9 @@ if test "x$ARCHTYPE" != xx86 -a "x$ARCHTYPE" != xppc; then
>  else
>  	APISRC=tests/api_$ARCHTYPE.h
>  fi
> +if test "x$ARCHTYPE" == xarmv7l; then
> +	CFLAGS="-mcpu=cortex-a9 -mtune=cortex-a9 -O2"
> +fi
>  
>  AC_SUBST(ARCHTYPE)
>  AC_SUBST(SUBARCHTYPE)
> diff --git a/urcu/arch_armv7l.h b/urcu/arch_armv7l.h
> new file mode 100644
> index 0000000..5920a4d
> --- /dev/null
> +++ b/urcu/arch_armv7l.h
> @@ -0,0 +1,59 @@
> +#ifndef _URCU_ARCH_ARMV7L_H
> +#define _URCU_ARCH_ARMV7L_H
> +
> +/*
> + * arch_unknown.h: trivial definitions for the "unknown" architecture.
> + *
> + * Copyright (c) 2010 Paul E. McKenney, IBM Corporation.
> + * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers at polymtl.ca>
> + *
> + * This library is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * This library 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
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with this library; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#include <urcu/compiler.h>
> +#include <urcu/config.h>
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif 
> +
> +/* We don't know, so guess!!! */
> +#define CACHE_LINE_SIZE	128
> +
> +#define mb()    asm volatile("dmb":::"memory")
> +
> +#include <stdlib.h>
> +#include <sys/time.h>
> +
> +typedef unsigned long long cycles_t;
> +
> +static inline cycles_t get_cycles (void)
> +{
> +	cycles_t thetime;
> +	struct timeval tv;
> +
> +	if (gettimeofday(&tv, NULL) != 0)
> +		return 0;
> +	thetime = ((cycles_t)tv.tv_sec) * 1000000ULL + ((cycles_t)tv.tv_usec);
> +	return (cycles_t)thetime;
> +}
> +
> +#ifdef __cplusplus 
> +}
> +#endif
> +
> +#include <urcu/arch_generic.h>
> +
> +#endif /* _URCU_ARCH_ARMV7L_H */
> diff --git a/urcu/uatomic_arch_armv7l.h b/urcu/uatomic_arch_armv7l.h
> new file mode 100644
> index 0000000..5eece49
> --- /dev/null
> +++ b/urcu/uatomic_arch_armv7l.h
> @@ -0,0 +1,48 @@
> +#ifndef _URCU_ARCH_UATOMIC_ARMV7L_H
> +#define _URCU_ARCH_UATOMIC_ARMV7L_H
> +
> +/* 
> + * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
> + * Copyright (c) 1996-1999 by Silicon Graphics.  All rights reserved.
> + * Copyright (c) 1999-2004 Hewlett-Packard Development Company, L.P.
> + * Copyright (c) 2009      Mathieu Desnoyers
> + * Copyright (c) 2010      Paul E. McKenney, IBM Corporation
> + *			   (Adapted from uatomic_arch_unknown.h)
> + *
> + * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
> + * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
> + *
> + * Permission is hereby granted to use or copy this program
> + * for any purpose,  provided the above notices are retained on all copies.
> + * Permission to modify the code and to distribute modified code is granted,
> + * provided the above notices are retained, and a notice that the code was
> + * modified is included with the above copyright notice.
> + *
> + * Code inspired from libuatomic_ops-1.2, inherited in part from the
> + * Boehm-Demers-Weiser conservative garbage collector.
> + */
> +
> +#include <urcu/compiler.h>
> +#include <urcu/system.h>
> +
> +#ifdef __cplusplus
> +extern "C" {
> +#endif 
> +
> +/* xchg */
> +#define uatomic_xchg(addr, v)	 __sync_lock_test_and_set(addr, v);

I expect that these __sync_*() operations have missing memory barriers ? It
might be safer to do something like:

#define uatomic_cmpxchg(addr, old _new) \
  {( \
     __typeof__(_new) __ret; \
     \
     smp_mb(); \
     __ret = __sync_val_compare_and_swap(addr, old, _new); \
     smp_mb(); \
    __ret;
  )}

(similar for other primitives)

The idea is that I don't trust gcc's __sync_*() implementation if they got the 
__sync_synchronize() wrong.

Thanks,

Mathieu

> +
> +/* cmpxchg */
> +#define uatomic_cmpxchg(addr, old, _new) \
> +	__sync_val_compare_and_swap(addr, old, _new)
> +
> +/* uatomic_add_return */
> +#define uatomic_add_return(addr, v)  __sync_add_and_fetch(addr, v)
> +
> +#ifdef __cplusplus 
> +}
> +#endif
> +
> +#include <urcu/uatomic_generic.h>
> +
> +#endif /* _URCU_ARCH_UATOMIC_ARMV7L_H */

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com