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authorAlex Bligh <alex@alex.org.uk>2013-08-21 16:02:44 +0100
committerStefan Hajnoczi <stefanha@redhat.com>2013-08-22 19:10:27 +0200
commitcd758dd0acaaf1f76f9727d4409915f3293db07a (patch)
treea7d393d3cb44bc46c4a28acc491a5a53fba1bd59
parent4e0c6529fcb5ccbed5eb2c4f094264eb447d49ea (diff)
aio / timers: Add prctl(PR_SET_TIMERSLACK, 1, ...) to reduce timer slack
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>
-rwxr-xr-xconfigure18
-rw-r--r--qemu-timer.c7
2 files changed, 25 insertions, 0 deletions
diff --git a/configure b/configure
index 56594121ad..0a55c20252 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 120d58fb2a..74f904b310 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)