GetTimeInMillis: spuport monotonic clock

Add support for CLOCK_MONOTONIC from clock_gettime, and use that in
GetTimeInMillis() if available, falling back to the old gettimeofday()
implementation.

This is _slightly_ faster on some 64-bit architectures, and _slightly_
slower on others (though barely measurable).
(cherry picked from d285833290316cb5dd1e7f1e52c96be3e9cf21cd commit)

3 files changed, 79 insertions, 6 deletions

diff --git a/configure.ac b/configure.ac
index 7945a272d..25570f2c0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -515,7 +515,7 @@ XEXT_LIB='$(top_builddir)/Xext/libXext.la'
 XEXTXORG_LIB='$(top_builddir)/Xext/libXextbuiltin.la'
 
 dnl Core modules for most extensions, et al.
-REQUIRED_MODULES="randrproto renderproto [fixesproto >= 4.0] damageproto xcmiscproto xextproto xproto xtrans xf86miscproto xf86vidmodeproto xf86bigfontproto [scrnsaverproto >= 1.1] bigreqsproto resourceproto fontsproto inputproto xf86dgaproto [kbproto >= 1.0.3]"
+REQUIRED_MODULES="randrproto renderproto [fixesproto >= 4.0] damageproto xcmiscproto xextproto [xproto >= 7.0.9] xtrans xf86miscproto xf86vidmodeproto xf86bigfontproto [scrnsaverproto >= 1.1] bigreqsproto resourceproto fontsproto inputproto xf86dgaproto [kbproto >= 1.0.3]"
 REQUIRED_LIBS="xfont xau fontenc"
 
 AM_CONDITIONAL(XV, [test "x$XV" = xyes])
@@ -873,9 +873,46 @@ PKG_CHECK_MODULES([XSERVERLIBS], [$REQUIRED_LIBS])
 
 XSERVER_CFLAGS="${XSERVERCFLAGS_CFLAGS}"
 XSERVER_LIBS="${XSERVERLIBS_LIBS} ${SYS_LIBS} -lm"
-AC_SUBST([XSERVER_LIBS])
 AC_SUBST([SYS_LIBS])
 
+AC_CHECK_FUNCS([clock_gettime], [have_clock_gettime=yes],
+               [AC_CHECK_LIB([rt], [clock_gettime], [have_clock_gettime=-lrt],
+                             [have_clock_gettime=no])])
+
+AC_MSG_CHECKING([for a useful monotonic clock ...])
+
+if ! test "x$have_clock_gettime" = xno; then
+    if ! test "x$have_clock_gettime" = xyes; then
+        LIBS="$have_clock_gettime"
+    else
+        LIBS=""
+    fi
+
+    AC_RUN_IFELSE([
+#define _POSIX_C_SOURCE 199309L
+#include <time.h>
+
+int main(int argc, char *argv[]) {
+    struct timespec tp;
+
+    if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+        return 0;
+    else
+        return 1;
+}
+    ], [MONOTONIC_CLOCK=yes], [MONOTONIC_CLOCK=no],
+       [MONOTONIC_CLOCK="cross compiling"])
+else
+    MONOTONIC_CLOCK=no
+fi
+
+AC_MSG_RESULT([$MONOTONIC_CLOCK])
+
+if test "x$MONOTONIC_CLOCK" = xyes; then
+    AC_DEFINE(MONOTONIC_CLOCK, 1, [Have monotonic clock from clock_gettime()])
+    XSERVER_LIBS="$XSERVER_LIBS $LIBS"
+fi
+
 dnl Imake defines SVR4 on SVR4 systems, and many files check for it, so
 dnl we need to replicate that here until those can all be fixed
 AC_MSG_CHECKING([if SVR4 needs to be defined])
@@ -890,6 +927,8 @@ AC_MSG_RESULT([yes])], AC_MSG_RESULT([no]))
 XSERVER_CFLAGS="$XSERVER_CFLAGS $CORE_INCS $XEXT_INC $COMPOSITE_INC $DAMAGE_INC $FIXES_INC $XI_INC $MI_INC $MIEXT_SHADOW_INC $MIEXT_LAYER_INC $MIEXT_DAMAGE_INC $RENDER_INC $RANDR_INC $FB_INC"
 AC_DEFINE_UNQUOTED(X_BYTE_ORDER,[$ENDIAN],[Endian order])
 
+AC_SUBST([XSERVER_LIBS])
+
 dnl ---------------------------------------------------------------------------
 dnl DDX section.
 dnl ---------------------------------------------------------------------------
diff --git a/include/dix-config.h.in b/include/dix-config.h.in
index 65c42e6af..35700e460 100644
--- a/include/dix-config.h.in
+++ b/include/dix-config.h.in
@@ -445,4 +445,7 @@
 /* Define to 1 if modules should avoid the libcwrapper */
 #undef NO_LIBCWRAPPER
 
+/* Have a monotonic clock from clock_gettime() */
+#undef MONOTONIC_CLOCK
+
 #endif /* _DIX_CONFIG_H_ */
diff --git a/os/utils.c b/os/utils.c
index 31ae26a18..379291c9d 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -53,6 +53,19 @@ OR PERFORMANCE OF THIS SOFTWARE.
 #include <dix-config.h>
 #endif
 
+/* The world's most shocking hack, to ensure we get clock_gettime() and
+ * CLOCK_MONOTONIC. */
+#ifdef _POSIX_C_SOURCE
+#define _SAVED_POSIX_C_SOURCE _POSIX_C_SOURCE
+#undef _POSIX_C_SOURCE
+#endif
+#define _POSIX_C_SOURCE 199309L
+#include <time.h>
+#undef _POSIX_C_SOURCE
+#ifdef _SAVED_POSIX_C_SOURCE
+#define _POSIX_C_SOURCE _SAVED_POSIX_C_SOURCE
+#endif
+
 #ifdef __CYGWIN__
 #include <stdlib.h>
 #include <signal.h>
@@ -92,7 +105,6 @@ OR PERFORMANCE OF THIS SOFTWARE.
 #if !defined(SYSV) && !defined(WIN32) && !defined(Lynx) && !defined(QNX4)
 #include <sys/resource.h>
 #endif
-#include <time.h>
 #include <sys/stat.h>
 #include <ctype.h>    /* for isspace */
 #include <stdarg.h>
@@ -256,6 +268,8 @@ int auditTrailLevel = 1;
 
 _X_EXPORT Bool Must_have_memory = FALSE;
 
+static int monotonic_usable = -1;
+
 #ifdef AIXV3
 int SyncOn  = 0;
 extern int SelectWaitTime;
@@ -535,10 +549,27 @@ GiveUp(int sig)
 _X_EXPORT CARD32
 GetTimeInMillis(void)
 {
-    struct timeval  tp;
+    struct timeval tv;
+#ifdef MONOTONIC_CLOCK
+    struct timespec tp;
+    int spare = 0;
+
+    if (_X_UNLIKELY(monotonic_usable == -1)) {
+        if (clock_gettime(0, &tp) == 0 &&
+            clock_getcpuclockid(0, &spare) == 0)
+            monotonic_usable = 1;
+        else
+            monotonic_usable = 0;
+    }
+
+    if (_X_LIKELY(monotonic_usable == 1)) {
+        if (clock_gettime(CLOCK_MONOTONIC, &tp) == 0)
+            return (tp.tv_sec * 1000) + (tp.tv_nsec / 1000000);
+    }
+#endif
 
-    X_GETTIMEOFDAY(&tp);
-    return(tp.tv_sec * 1000) + (tp.tv_usec / 1000);
+    X_GETTIMEOFDAY(&tv);
+    return(tv.tv_sec * 1000) + (tv.tv_usec / 1000);
 }
 
 _X_EXPORT void