From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:59335)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@redhat.com>) id 1VCbF2-0003h0-26
	for qemu-devel@nongnu.org; Thu, 22 Aug 2013 16:12:30 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <stefanha@redhat.com>) id 1VCbEx-0004Mu-1E
	for qemu-devel@nongnu.org; Thu, 22 Aug 2013 16:12:23 -0400
Received: from mx1.redhat.com ([209.132.183.28]:49652)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <stefanha@redhat.com>) id 1VCbEw-0004Mj-PB
	for qemu-devel@nongnu.org; Thu, 22 Aug 2013 16:12:18 -0400
From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Thu, 22 Aug 2013 22:11:10 +0200
Message-Id: <1377202298-22896-15-git-send-email-stefanha@redhat.com>
In-Reply-To: <1377202298-22896-1-git-send-email-stefanha@redhat.com>
References: <1377202298-22896-1-git-send-email-stefanha@redhat.com>
Subject: [Qemu-devel] [PULL 14/42] aio / timers: Add prctl(PR_SET_TIMERSLACK,
	1, ...) to reduce timer slack
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: qemu-devel@nongnu.org
Cc: Stefan Hajnoczi <stefanha@redhat.com>, Alex Bligh <alex@alex.org.uk>, Anthony Liguori <anthony@codemonkey.ws>

From: Alex Bligh <alex@alex.org.uk>

Where supported, called prctl(PR_SET_TIMERSLACK, 1, ...) to
set one nanosecond timer slack to increase precision of timer
calls.

Signed-off-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 configure    | 18 ++++++++++++++++++
 qemu-timer.c |  7 +++++++
 2 files changed, 25 insertions(+)

diff --git a/configure b/configure
index 5659412..0a55c20 100755
--- a/configure
+++ b/configure
@@ -2834,6 +2834,21 @@ if compile_prog "" "" ; then
   ppoll=yes
 fi
 
+# check for prctl(PR_SET_TIMERSLACK , ... ) support
+prctl_pr_set_timerslack=no
+cat > $TMPC << EOF
+#include <sys/prctl.h>
+
+int main(void)
+{
+    prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
+    return 0;
+}
+EOF
+if compile_prog "" "" ; then
+  prctl_pr_set_timerslack=yes
+fi
+
 # check for epoll support
 epoll=no
 cat > $TMPC << EOF
@@ -3833,6 +3848,9 @@ fi
 if test "$ppoll" = "yes" ; then
   echo "CONFIG_PPOLL=y" >> $config_host_mak
 fi
+if test "$prctl_pr_set_timerslack" = "yes" ; then
+  echo "CONFIG_PRCTL_PR_SET_TIMERSLACK=y" >> $config_host_mak
+fi
 if test "$epoll" = "yes" ; then
   echo "CONFIG_EPOLL=y" >> $config_host_mak
 fi
diff --git a/qemu-timer.c b/qemu-timer.c
index 120d58f..74f904b 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -41,6 +41,10 @@
 #include <poll.h>
 #endif
 
+#ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
+#include <sys/prctl.h>
+#endif
+
 /***********************************************************/
 /* timers */
 
@@ -507,6 +511,9 @@ void init_clocks(void)
         vm_clock = qemu_clock_new(QEMU_CLOCK_VIRTUAL);
         host_clock = qemu_clock_new(QEMU_CLOCK_HOST);
     }
+#ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
+    prctl(PR_SET_TIMERSLACK, 1, 0, 0, 0);
+#endif
 }
 
 uint64_t timer_expire_time_ns(QEMUTimer *ts)
-- 
1.8.3.1