Align inter-thread shared structers on cache-line granularity

Specifically ypipe_t specializations for msg_t and command_t.

Currently only supports platforms where posix_memalign is available.

configure.ac

@@ -271,7 +271,7 @@ case "${host_os}" in
         CPPFLAGS="-D_GNU_SOURCE $CPPFLAGS"
         AC_DEFINE(ZMQ_HAVE_CYGWIN, 1, [Have Cygwin])
         libzmq_on_cygwin="yes"
-        libzmq_dso_visibility="no"        
+        libzmq_dso_visibility="no"
         if test "x$enable_static" = "xyes"; then
             AC_MSG_ERROR([Building static libraries is not supported under Cygwin])
         fi
@@ -436,10 +436,10 @@ AM_CONDITIONAL(HAVE_PGM, test "x$have_pgm_library" = "xyes")
 # This uses "--with-norm" to point to the "norm" directory
 # for "norm/include" and "norm/lib"
 #(if "--with-norm=yes" is given, then assume installed on system)
-AC_ARG_WITH([norm], 
-    [AS_HELP_STRING([--with-norm], 
+AC_ARG_WITH([norm],
+    [AS_HELP_STRING([--with-norm],
         [build libzmq with NORM protocol extension, optionally specifying norm path [default=no]])],
-    [with_norm_ext=$withval], 
+    [with_norm_ext=$withval],
     [with_norm_ext=no])
 
 
@@ -481,7 +481,7 @@ AM_CONDITIONAL(ON_LINUX, test "x$libzmq_on_linux" = "xyes")
 
 # Checks for library functions.
 AC_TYPE_SIGNAL
-AC_CHECK_FUNCS(perror gettimeofday clock_gettime memset socket getifaddrs freeifaddrs fork)
+AC_CHECK_FUNCS(perror gettimeofday clock_gettime memset socket getifaddrs freeifaddrs fork posix_memalign)
 AC_CHECK_HEADERS([alloca.h])
 
 LIBZMQ_CHECK_SOCK_CLOEXEC([

src/command.hpp

@@ -146,8 +146,12 @@ namespace zmq
             } done;
 
         } args;
+
+        enum { pad_size = 64 - (sizeof(destination) + sizeof(args)) };
+        unsigned char unused[ pad_size ];
+
     };
 
-}    
+}
 
 #endif

src/yqueue.hpp

@@ -33,7 +33,7 @@ namespace zmq
     //  to minimise number of allocations/deallocations needed. Thus yqueue
     //  allocates/deallocates elements in batches of N.
     //
-    //  yqueue allows one thread to use push/back function and another one 
+    //  yqueue allows one thread to use push/back function and another one
     //  to use pop/front functions. However, user must ensure that there's no
     //  pop on the empty queue and that both threads don't access the same
     //  element in unsynchronised manner.
@@ -41,8 +41,16 @@ namespace zmq
     //  T is the type of the object in the queue.
     //  N is granularity of the queue (how many pushes have to be done till
     //  actual memory allocation is required).
-
+#ifdef HAVE_POSIX_MEMALIGN
+    // ALIGN is the memory alignment size to use in the case where we have
+    // posix_memalign available. Default value is 64, this alignment will
+    // prevent two queue chunks from occupying the same CPU cache line on
+    // architectures where cache lines are <= 64 bytes (e.g. most things
+    // except POWER).
+    template <typename T, int N, size_t ALIGN = 64> class yqueue_t
+#else
     template <typename T, int N> class yqueue_t
+#endif
     {
     public:
 
@@ -65,7 +73,7 @@ namespace zmq
                 if (begin_chunk == end_chunk) {
                     free (begin_chunk);
                     break;
-                } 
+                }
                 chunk_t *o = begin_chunk;
                 begin_chunk = begin_chunk->next;
                 free (o);
@@ -103,7 +111,13 @@ namespace zmq
                 end_chunk->next = sc;
                 sc->prev = end_chunk;
             } else {
+#ifdef HAVE_POSIX_MEMALIGN
+                void *pv;
+                if (posix_memalign(&pv, ALIGN, sizeof (chunk_t)) == 0)
+                    end_chunk->next = (chunk_t*) pv;
+#else
                 end_chunk->next = (chunk_t*) malloc (sizeof (chunk_t));
+#endif
                 alloc_assert (end_chunk->next);
                 end_chunk->next->prev = end_chunk;
             }