Re: [Boost-bugs] [Boost C++ Libraries] #6308: Add sp_counted_base_aix.hpp using AIX atomic operations

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6308: Add sp_counted_base_aix.hpp using AIX atomic operations
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2011-12-23 13:18:36

#6308: Add sp_counted_base_aix.hpp using AIX atomic operations
-----------------------------------------+----------------------------------
  Reporter:  aaron.riekenberg@…          |       Owner:  pdimov      
      Type:  Feature Requests            |      Status:  reopened    
 Milestone:  To Be Determined            |   Component:  smart_ptr   
   Version:  Boost 1.48.0                |    Severity:  Optimization
Resolution:                              |    Keywords:              
-----------------------------------------+----------------------------------

Comment (by aaron.riekenberg@…):

 AIX only runs on POWER and PowerPC.

 fetch_and_add is not documented to do any memory barrier.  I looked at the
 instructions for fetch_and_add with listi in dbx.  It does lwarx and stwcx
 but does not do lwsync, sync, or isync.  So I believe it does not contain
 a barrier.

 I am attaching a new version of sp_counted_base_aix.hpp
 (sp_counted_base_aix_122311.hpp).  This version is written more in the
 style of sp_counted_base_gcc_ppc.hpp.  I added a leading sync instruction
 to atomic_decrement and a trailing isync for a full barrier.

 The performance of this version is a bit worse than my original no-barrier
 version.  Each iteration of the test program now takes about 8.8
 microseconds.  This is still 2.5X faster than using pthread_mutex.

 Thanks for your patience in getting this correct.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6308#comment:5>
Boost C++ Libraries <http://www.boost.org/>
Boost provides free peer-reviewed portable C++ source libraries.