Re: [PATCH] Unify pthread_spin_[try]lock implementations.

[Carlos O'Donell <carlos_odonell at mentor dot com>]

On 8/14/2012 11:16 PM, Maxim Kuvyrkov wrote:
> On 26/07/2012, at 6:13 AM, Roland McGrath wrote:
> 
>> Here I think the reasonable thing to do is:
>>
>> /* A machine-specific version can define SPIN_LOCK_READS_BETWEEN_CMPXCHG
>>   to the number of plain reads that it's optimal to spin on between uses
>>   of atomic_compare_and_exchange_val_acq.  If spinning forever is optimal
>>   then use -1.  If no plain reads here would ever be optimal, use 0.  */
>> #ifndef SPIN_LOCK_READS_BETWEEN_CMPXCHG
>> # warning machine-dependent file should define SPIN_LOCK_READS_BETWEEN_CMPXCHG
>> # define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
>> #endif
>>
>> Then ARM et al can do:
>>
>> /* Machine-dependent rationale about the selection of this value.  */
>> #define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
>> #include <nptl/pthread_spin_lock.c>
>>
>> while Teil will use -1.
>>
>>> +      if (PTHREAD_SPIN_LOCK_WAIT)
>>
>> Don't use implicit boolean coercion.
>> Use "if (SPIN_LOCK_READS_BETWEEN_CMPXCHG >= 0)".
>>
>>> +	{
>>> +	  int wait = PTHREAD_SPIN_LOCK_WAIT;
>>> +
>>> +	  while (*lock != 0 && --wait)
>>> +	    ;
>>
>> Write it:
>> 	while (wait > 0 && *lock != 0)
>> 	  --wait;
>>
>> That handles the SPIN_LOCK_READS_BETWEEN_CMPXCHG==0 case implicitly,
>> avoids the ugly empty statement, and doesn't use implicit coercion.
> 
> OK, the updated patch attached.  Is this what you had in mind?
> 
> As before the patch touches ARM, HPPA, M68K and MIPS.
> 
> The patch also adds another optimization to use atomic_exchange_acq for the first attempt at acquiring the lock.  For a free lock atomic_exchange is, generally, faster; while atomic_compare_and_exchange is better for waiting on a contended lock.  Same rationale applies to pthread_spin_trylock.
> 
> This patch builds on MIPS and regression testing is in progress.  OK to apply is tests are fine?
> 
> Thank you,
> 
> --
> Maxim Kuvyrkov
> CodeSourcery / Mentor Graphics
> 
> 
> Add generic versions of pthread_spin_lock and pthread_spin_trylock.
> 
> 	2012-07-09  Maxim Kuvyrkov  <maxim@codesourcery.com>
> 
> 	* nptl/pthread_spin_lock.c: New file.
> 	* nptl/pthread_spin_trylock.c: New file.
> 
> 	ports/
> 	* sysdeps/arm/nptl/pthread_spin_lock.c: Use generic code.
> 	* sysdeps/arm/nptl/pthread_spin_trylock.c: Remove, use generic version.
> 
> 	* sysdeps/hppa/nptl/pthread_spin_lock.c: Use generic code.
> 	* sysdeps/hppa/nptl/pthread_spin_trylock.c: Remove, use generic version.
> 
> 	* sysdeps/m68k/nptl/pthread_spin_lock.c: Use generic code.
> 	* sysdeps/m68k/nptl/pthread_spin_trylock.c: Remove, use generic version.
> 
> 	* sysdeps/mips/nptl/pthread_spin_lock.S: Remove, use generic version.
> 	* sysdeps/mips/nptl/pthread_spin_lock.c: New file.
> 	* sysdeps/mips/nptl/pthread_spin_trylock.S: Remove, use generic version.
> ---
>  nptl/pthread_spin_lock.c                       |   69 ++++++++++++++++++++++++
>  nptl/pthread_spin_trylock.c                    |   27 +++++++++
>  ports/sysdeps/arm/nptl/pthread_spin_lock.c     |   16 +-----
>  ports/sysdeps/arm/nptl/pthread_spin_trylock.c  |   26 ---------
>  ports/sysdeps/hppa/nptl/pthread_spin_lock.c    |   24 +-------
>  ports/sysdeps/hppa/nptl/pthread_spin_trylock.c |   33 -----------
>  ports/sysdeps/m68k/nptl/pthread_spin_lock.c    |   16 +-----
>  ports/sysdeps/m68k/nptl/pthread_spin_trylock.c |   27 ---------
>  ports/sysdeps/mips/nptl/pthread_spin_lock.S    |   36 ------------
>  ports/sysdeps/mips/nptl/pthread_spin_lock.c    |   19 +++++++
>  ports/sysdeps/mips/nptl/pthread_spin_trylock.S |   40 --------------
>  11 files changed, 124 insertions(+), 209 deletions(-)
>  create mode 100644 nptl/pthread_spin_lock.c
>  create mode 100644 nptl/pthread_spin_trylock.c
>  delete mode 100644 ports/sysdeps/arm/nptl/pthread_spin_trylock.c
>  delete mode 100644 ports/sysdeps/hppa/nptl/pthread_spin_trylock.c
>  delete mode 100644 ports/sysdeps/m68k/nptl/pthread_spin_trylock.c
>  delete mode 100644 ports/sysdeps/mips/nptl/pthread_spin_lock.S
>  create mode 100644 ports/sysdeps/mips/nptl/pthread_spin_lock.c
>  delete mode 100644 ports/sysdeps/mips/nptl/pthread_spin_trylock.S
> 
> diff --git a/ports/sysdeps/hppa/nptl/pthread_spin_lock.c b/ports/sysdeps/hppa/nptl/pthread_spin_lock.c
> index bcf2240..7c86768 100644
> --- a/ports/sysdeps/hppa/nptl/pthread_spin_lock.c
> +++ b/ports/sysdeps/hppa/nptl/pthread_spin_lock.c
> @@ -1,4 +1,4 @@
> -/* Copyright (C) 2005 Free Software Foundation, Inc.
> +/* Copyright (C) 2005-2012 Free Software Foundation, Inc.
>     This file is part of the GNU C Library.
>  
>     The GNU C Library is free software; you can redistribute it and/or
> @@ -15,23 +15,5 @@
>     License along with the GNU C Library.  If not, see
>     <http://www.gnu.org/licenses/>.  */
>  
> -#include <atomic.h>
> -#include "pthreadP.h"
> -
> -int
> -pthread_spin_lock (pthread_spinlock_t *lock)
> -{
> -#if 0
> -  volatile unsigned int *addr = __ldcw_align (lock);
> -
> -  while (__ldcw (addr) == 0)
> -    while (*addr == 0) ;
> -
> -  return 0;
> -#endif
> -
> -  while (atomic_compare_and_exchange_val_acq(lock, 1, 0) == 1)
> -    while (*lock == 1);
> -  
> -  return 0;
> -}
> +#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
> +#include_next <nptl/pthread_spin_lock.c>

OK for hppa.

> diff --git a/ports/sysdeps/hppa/nptl/pthread_spin_trylock.c b/ports/sysdeps/hppa/nptl/pthread_spin_trylock.c
> deleted file mode 100644
> index a802861..0000000
> --- a/ports/sysdeps/hppa/nptl/pthread_spin_trylock.c
> +++ /dev/null
> @@ -1,33 +0,0 @@
> -/* Copyright (C) 2005 Free Software Foundation, Inc.
> -   This file is part of the GNU C Library.
> -
> -   The GNU C 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.
> -
> -   The GNU C 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 the GNU C Library.  If not, see
> -   <http://www.gnu.org/licenses/>.  */
> -
> -#include <errno.h>
> -#include <atomic.h>
> -#include "pthreadP.h"
> -
> -int
> -pthread_spin_trylock (pthread_spinlock_t *lock)
> -{
> -#if 0
> -  volatile unsigned int *a = __ldcw_align (lock);
> -
> -  return __ldcw (a) ? 0 : EBUSY;
> -#endif
> -
> -  return atomic_compare_and_exchange_val_acq(lock, 1, 0) ? EBUSY : 0;
> -
> -}

OK for hppa.

Cheers,
Carlos.
-- 
Carlos O'Donell
Mentor Graphics / CodeSourcery
carlos_odonell@mentor.com
carlos@codesourcery.com
+1 (613) 963 1026