Re: [PING][PATCH v3] PowerPC: libc single-thread lock optimization

["Tulio Magno Quites Machado Filho" <tuliom at linux dot vnet dot ibm dot com>]

Ping!

Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com> writes:

> I continued the work started by Adhemerval.  The discussion around version 2
> of this patch is available at http://patchwork.sourceware.org/patch/2516/
>
> Nowadays, we already require GCC 4.7, so we can safely rely on compiler
> built-ins for most of our atomic primitives.
>
> Changes since v2:
>  - Updated ChangeLog and commit message.
>  - Replaced the following atomic primitives by compiler built-ins:
>    exchange*, and* and or*.
>
> ---8<---
>
> Add relaxed atomics as a lock optimization.  Addressing the concerns
> raised in previous discussions, the primitives are still signal-safe
> (although not thread-safe), so if future implementations relying on
> this code (e.g. malloc) is changed to be async-safe, it won't require to
> adjust powerpc atomics.
>
> For catomic_and and catomic_or I follow the definition at 'include/atomic.h'
> (which powerpc is currently using) and implemented the atomics with acquire
> semantics.  The new implementation is based on compiler built-ins.
>
> On synthetic benchmarks it shows an improvement of 5-10% for malloc
> calls and a performance increase of 7-8% in 483.xalancbmk from
> speccpu2006 (number from a POWER8 machine).
>
> Checked on powerpc32, powerpc64 and powerpc64le.
>
> 2016-03-11  Adhemerval Zanella Netto  <azanella@linux.vnet.ibm.com>
>             Tulio Magno Quites Machado Filho  <tuliom@linux.vnet.ibm.com>
>
> 	* malloc/malloc.c (malloc_consolidate): Replace 0 by NULL in
> 	order to match the type of p when calling atomic_exchange_acq().
> 	* sysdeps/powerpc/atomic-machine.h
> 	(__arch_atomic_exchange_32_acq): Removed.
> 	(__arch_atomic_exchange_32_rel): Likewise
> 	(__arch_compare_and_exchange_val_32_relaxed): New macro: atomic compare
> 	and exchange with relaxed semantic.
> 	(atomic_compare_and_exchange_val_relaxed): Likewise.
> 	(__atomic_is_single_thread): New macro: check if program is
> 	single-thread.
> 	(atomic_compare_and_exchange_val_acq): Add relaxed operation for
> 	single-thread.
> 	(atomic_compare_and_exchange_val_rel): Likewise.
> 	(atomic_exchange_acq): Likewise.
> 	(atomic_exchange_rel): Likewise.
> 	(catomic_and): Add relaxed operation and use compiler built-ins.
> 	(catomic_or): Likewise.
> 	(atomic_exchange_acq): Modify to use compiler built-ins.
> 	(atomic_exchange_rel): Likewise.
> 	* sysdeps/powerpc/powerpc32/atomic-machine.h
> 	(__arch_compare_and_exchange_val_64_relaxed): New macro: add empty
> 	implementation.
> 	(__arch_atomic_exchange_64_relaxed): Likewise.
> 	* sysdeps/powerpc/powerpc64/atomic-machine.h
> 	(__arch_compare_and_exchange_val_64_relaxed): New macro: atomic compare
> 	and exchange with relaxed semantics.
> 	(__arch_atomic_exchange_64_acq): Removed.
> 	(__arch_atomic_exchange_64_rel): Removed.

-- 
Tulio Magno