force IPC/shmem based shared memory.
#endif
+/* if we have both SYSV IPC and shared mmap then we need to choose. For most
+ systems it is much faster to use SYSV IPC, but under Linux it is
+ about 5 times faster to use fcntl, so for Linux systems we force
+ fcntl based locking */
+#if (defined(HAVE_SYSV_IPC) && defined(HAVE_SHARED_MMAP))
+# ifdef LINUX
+# undef HAVE_SYSV_IPC
+# else
+# undef HAVE_SHARED_MMAP
+# endif
+#endif
+
+
#include <sys/types.h>
#ifdef TIME_WITH_SYS_TIME