Luca Tettamanti wrote:
[snip]
> I've implemented some of my suggestions in the following patch - rebased
> to kvm-userspace current git since it's easier to test (...ok, I'm lazy -
> but you get the idea):
>
>
> diff --git a/qemu/configure b/qemu/configure
> index 365b7fb..38373db 100755
> --- a/qemu/configure
> +++ b/qemu/configure
> @@ -262,6 +262,8 @@ for opt do
> ;;
> --enable-uname-release=*) uname_release="$optarg"
> ;;
> + --disable-dynamic-ticks) dynamic_ticks="no"
> + ;;
Is there a situation where the attempt to use dynticks is harmful?
> esac
> done
>
> @@ -788,6 +790,9 @@ echo "TARGET_DIRS=$target_list" >> $config_mak
> if [ "$build_docs" = "yes" ] ; then
> echo "BUILD_DOCS=yes" >> $config_mak
> fi
> +if test "$dynamic_ticks" != "no" ; then
> + echo "#define DYNAMIC_TICKS 1" >> $config_h
> +fi
>
> # XXX: suppress that
> if [ "$bsd" = "yes" ] ; then
> diff --git a/qemu/vl.c b/qemu/vl.c
> index 4b73f77..05639d7 100644
> --- a/qemu/vl.c
> +++ b/qemu/vl.c
> @@ -759,6 +759,35 @@ static unsigned int period = 1;
> static int timer_freq;
> #endif
>
> +#ifdef DYNAMIC_TICKS
> +/* If DYNAMIC_TICKS is defined (and use_dynamic_ticks selected) qemu does not
> + * attepmt to generate SIGALRM at a constant rate. Rather, the system timer
> is
> + * set to generate SIGALRM only when it is needed. DYNAMIC_TICKS reduces the
> + * number of SIGALRMs sent to idle dynamic-ticked guests. */
> +
> +static void rearm_host_timer(void);
> +static int dynticks_create_timer(void);
> +
> +static int use_dynticks = 1;
> +
> +static int use_dynamic_ticks() {
> + return use_dynticks;
> +}
> +
> +#else
> +
> +static void rearm_host_timer(void) {}
> +
> +static int dynticks_create_timer(void) {
> + return 0;
> +}
> +
> +static int use_dynamic_ticks() {
> + return 0;
> +}
> +
> +#endif
This optimization is probably not worth an #ifdef.
> +
> QEMUClock *qemu_new_clock(int type)
> {
> QEMUClock *clock;
> @@ -803,6 +832,7 @@ void qemu_del_timer(QEMUTimer *ts)
> }
> pt = &t->next;
> }
> + rearm_host_timer();
> }
>
> /* modify the current timer so that it will be fired when current_time
> @@ -862,6 +892,7 @@ static void qemu_run_timers(QEMUTimer **ptimer_head,
> int64_t current_time)
> /* run the callback (the timer list can be modified) */
> ts->cb(ts->opaque);
> }
> + rearm_host_timer();
> }
>
> int64_t qemu_get_clock(QEMUClock *clock)
> @@ -969,7 +1000,8 @@ static void host_alarm_handler(int host_signum)
> last_clock = ti;
> }
> #endif
> - if (qemu_timer_expired(active_timers[QEMU_TIMER_VIRTUAL],
> + if (use_dynamic_ticks() ||
> + qemu_timer_expired(active_timers[QEMU_TIMER_VIRTUAL],
> qemu_get_clock(vm_clock)) ||
> qemu_timer_expired(active_timers[QEMU_TIMER_REALTIME],
> qemu_get_clock(rt_clock))) {
> @@ -1126,21 +1158,26 @@ static void init_timer_alarm(void)
> act.sa_handler = host_alarm_handler;
> sigaction(SIGALRM, &act, NULL);
>
> - itv.it_interval.tv_sec = 0;
> - itv.it_interval.tv_usec = 999; /* for i386 kernel 2.6 to get 1 ms */
> - itv.it_value.tv_sec = 0;
> - itv.it_value.tv_usec = 10 * 1000;
> - setitimer(ITIMER_REAL, &itv, NULL);
> - /* we probe the tick duration of the kernel to inform the user if
> - the emulated kernel requested a too high timer frequency */
> - getitimer(ITIMER_REAL, &itv);
> + if (use_dynamic_ticks() && dynticks_create_timer()) {
Maybe
dynticks_create_timer();
if (!use_dynamic_ticks()) {
...
is a bit clearer. Or maybe put both alternatives in a create_timer()
function.
> + /* dynticks disabled or failed to create a timer, fallback
> + * to old code.
> + */
> + itv.it_interval.tv_sec = 0;
> + itv.it_interval.tv_usec = 999; /* for i386 kernel 2.6 to get 1
> ms */
> + itv.it_value.tv_sec = 0;
> + itv.it_value.tv_usec = 10 * 1000;
> + setitimer(ITIMER_REAL, &itv, NULL);
> + /* we probe the tick duration of the kernel to inform the user if
> + the emulated kernel requested a too high timer frequency */
> + getitimer(ITIMER_REAL, &itv);
> + }
>
> #if defined(__linux__)
> /* XXX: force /dev/rtc usage because even 2.6 kernels may not
> have timers with 1 ms resolution. The correct solution will
> be to use the POSIX real time timers available in recent
> 2.6 kernels */
> - if (itv.it_interval.tv_usec > 1000 || 1) {
> + if (!use_dynamic_ticks() && (itv.it_interval.tv_usec > 1000 || 1)) {
> /* try to use /dev/rtc to have a faster timer */
> if ((!use_rtc && !use_hpet) || (start_rtc_timer() < 0))
> goto use_itimer;
> @@ -6110,6 +6147,7 @@ void vm_start(void)
> cpu_enable_ticks();
> vm_running = 1;
> vm_state_notify(1);
> + rearm_host_timer();
> }
> }
>
> @@ -6536,6 +6574,9 @@ void help(void)
> "-no-rtc don't use /dev/rtc for timer alarm (do use
> gettimeofday)\n"
> "-use-hpet use /dev/hpet (HPET) instead of RTC for timer
> alarm\n"
> #endif
> +#ifdef DYNAMIC_TICKS
> + "-no-dyntick don't use dynamic ticks\n"
> +#endif
> "-option-rom rom load a file, rom, into the option ROM space\n"
> "\n"
> "During emulation, the following keys are useful:\n"
> @@ -6630,6 +6671,9 @@ enum {
> QEMU_OPTION_use_hpet,
> #endif
> QEMU_OPTION_cpu_vendor,
> +#ifdef DYNAMIC_TICKS
> + QEMU_OPTION_no_dyntick,
> +#endif
> };
>
> typedef struct QEMUOption {
> @@ -6728,6 +6772,9 @@ const QEMUOption qemu_options[] = {
> { "use-hpet", 0, QEMU_OPTION_use_hpet },
> #endif
> { "cpu-vendor", HAS_ARG, QEMU_OPTION_cpu_vendor },
> +#if defined(DYNAMIC_TICKS)
> + { "no-dyntick", 0, QEMU_OPTION_no_dyntick },
> +#endif
> { NULL },
> };
>
> @@ -6932,6 +6979,78 @@ static BOOL WINAPI qemu_ctrl_handler(DWORD type)
>
> #define MAX_NET_CLIENTS 32
>
> +#ifdef DYNAMIC_TICKS
> +
> +static timer_t host_timer;
> +
> +static int dynticks_create_timer() {
> + struct sigevent ev;
> +
> + ev.sigev_value.sival_int = 0;
> + ev.sigev_notify = SIGEV_SIGNAL;
> + ev.sigev_signo = SIGALRM;
> +
> + if (timer_create(CLOCK_REALTIME, &ev, &host_timer)) {
> + perror("timer_create");
> +
> + /* disable dynticks */
> + fprintf(stderr, "Dynamic Ticks disabled\n");
> + use_dynticks = 0;
> +
> + return -1;
> + }
> +
> + return 0;
> +}
> +
> +/* call host_alarm_handler just when the nearest QEMUTimer expires */
> +/* expire_time is measured in nanosec for vm_clock but in millisec
> + * for rt_clock
> + */
> +static void rearm_host_timer(void) {
> + struct itimerspec timeout;
> + int64_t nearest_delta_us = INT64_MAX;
> +
> + if (!use_dynamic_ticks())
> + return;
> +
> + if (active_timers[QEMU_TIMER_REALTIME] ||
> + active_timers[QEMU_TIMER_VIRTUAL]) {
> + int64_t vmdelta_us, current_us;
> +
> + if (active_timers[QEMU_TIMER_REALTIME])
> + nearest_delta_us =
> (active_timers[QEMU_TIMER_REALTIME]->expire_time -
> qemu_get_clock(rt_clock))*1000;
> +
> + if (active_timers[QEMU_TIMER_VIRTUAL]) {
> + /* round up */
> + vmdelta_us = (active_timers[QEMU_TIMER_VIRTUAL]->expire_time -
> qemu_get_clock(vm_clock)+999)/1000;
> + if (vmdelta_us < nearest_delta_us)
> + nearest_delta_us = vmdelta_us;
> + }
> +
> + /* Avoid arming the timer to negative, zero, or too low values */
> + /* MIN_TIMER_REARM_US should be optimized */
> +#define MIN_TIMER_REARM_US 250
> + if (nearest_delta_us <= MIN_TIMER_REARM_US)
> + nearest_delta_us = MIN_TIMER_REARM_US;
> +
> + /* check whether a timer is already running */
> + if (timer_gettime(host_timer, &timeout))
> + perror("gettime");
... and exit() ?
> + current_us = timeout.it_value.tv_sec * 1000000 +
> timeout.it_value.tv_nsec/1000;
> + if (current_us && current_us <= nearest_delta_us)
> + return;
> +
> + timeout.it_interval.tv_sec = 0;
> + timeout.it_interval.tv_nsec = 0; /* 0 for one-shot timer */
> + timeout.it_value.tv_sec = nearest_delta_us / 1000000;
> + timeout.it_value.tv_nsec = nearest_delta_us % 1000000 * 1000;
> + if (timer_settime(host_timer, 0 /* RELATIVE */, &timeout, NULL))
> + perror("settime");
Likewise here.
> + }
> +}
> +#endif /* DYNAMIC_TICKS */
> +
> static int saved_argc;
> static char **saved_argv;
>
> @@ -7457,6 +7576,11 @@ int main(int argc, char **argv)
> case QEMU_OPTION_cpu_vendor:
> cpu_vendor_string = optarg;
> break;
> +#ifdef DYNAMIC_TICKS
> + case QEMU_OPTION_no_dyntick:
> + use_dynticks = 0;
> + break;
> +#endif
> }
> }
> }
>
> Luca
> --
> Se non puoi convincerli, confondili.
>
>
>
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