[ltt-dev] [PATCH RFC] Native ARM7L support
Paul E. McKenney
paulmck at linux.vnet.ibm.com
Fri Jun 18 14:23:42 EDT 2010
On Sun, Jun 13, 2010 at 10:12:20PM -0400, Mathieu Desnoyers wrote:
> * Paul E. McKenney (paulmck at linux.vnet.ibm.com) wrote:
> > On Sun, Jun 13, 2010 at 06:01:29PM -0400, Mathieu Desnoyers wrote:
> > > * 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 ?)
> >
> > Might be. In this case, the definition of "freaking slow" is >40ns for
> > an empty loop. Though I suspect that getting call_rcu() working would
> > be higher priority, and I believe that I have a reasonable approach.
> >
> > And we are going to need a few RCU-based data structures as well.
>
> Yep, the next things on the urcu wishlist IMHO would be:
>
> 1) call_rcu() implementation, derived from defer_rcu() code if appropriate.
I have some ideas along this line, and could put together a patch
if you would like.
> 2) RCU hash tables & RCU binary trees & RCU queues (with lock-free push/pop)
> (& stack?)
>
> There is already some code that exists for most of these, but I'd like to be
> comfortable with the implementations (and ideally have some proof that they
> actually work) before merging them.
I do see the rbtree branch and the various list macros. I do have a few
simple RCU-protected stack/queue things. Josh Triplett has done some
resizable hash-table work, as has Herbert Xu. But if they aren't up for
it, I could see what I can do.
Thanx, Paul
> Thoughts ?
>
> Thanks,
>
> Mathieu
>
> >
> > > 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.
> >
> > Then there is the question as to whether they used atomics instructions.
> > Sigh!
> >
> > I will run some tests and see what I learn. (Busted disassemblers, but
> > I might yet need to hand-decode the instructions...)
> >
> > Thanx, Paul
> >
> > > 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
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
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