Commit cd758dd0 authored by Alex Bligh's avatar Alex Bligh Committed by Stefan Hajnoczi
Browse files

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: default avatarAlex Bligh <alex@alex.org.uk>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 4e0c6529

configure

+18 −0
Original line number Diff line number Diff line
@@ -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

qemu-timer.c

+7 −0
Original line number Diff line number Diff line
@@ -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)