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aio / timers: Add prctl(PR_SET_TIMERSLACK, 1, ...) to reduce timer slack

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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>
This commit is contained in:
Alex Bligh 2013-08-21 16:02:44 +01:00 committed by Stefan Hajnoczi
parent 4e0c6529fc
commit cd758dd0ac
2 changed files with 25 additions and 0 deletions
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18
configure vendored
View File

@ -2834,6 +2834,21 @@ if compile_prog "" "" ; then
ppoll=yes ppoll=yes
fi 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 # check for epoll support
epoll=no epoll=no
cat > $TMPC << EOF cat > $TMPC << EOF
@ -3833,6 +3848,9 @@ fi
if test "$ppoll" = "yes" ; then if test "$ppoll" = "yes" ; then
echo "CONFIG_PPOLL=y" >> $config_host_mak echo "CONFIG_PPOLL=y" >> $config_host_mak
fi fi
if test "$prctl_pr_set_timerslack" = "yes" ; then
echo "CONFIG_PRCTL_PR_SET_TIMERSLACK=y" >> $config_host_mak
fi
if test "$epoll" = "yes" ; then if test "$epoll" = "yes" ; then
echo "CONFIG_EPOLL=y" >> $config_host_mak echo "CONFIG_EPOLL=y" >> $config_host_mak
fi fi

7
qemu-timer.c
View File

@ -41,6 +41,10 @@
#include <poll.h> #include <poll.h>
#endif #endif
#ifdef CONFIG_PRCTL_PR_SET_TIMERSLACK
#include <sys/prctl.h>
#endif
/***********************************************************/ /***********************************************************/
/* timers */ /* timers */
@ -507,6 +511,9 @@ void init_clocks(void)
vm_clock = qemu_clock_new(QEMU_CLOCK_VIRTUAL); vm_clock = qemu_clock_new(QEMU_CLOCK_VIRTUAL);
host_clock = qemu_clock_new(QEMU_CLOCK_HOST); 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) uint64_t timer_expire_time_ns(QEMUTimer *ts)