[PULL,3/7] balloon: re-enable balloon stats

The statistics are now available through device properties via a
polling mechanism. First a client has to enable polling, then it
can query available stats.

Polling is enabled by setting an update interval (in seconds)
to a property named guest-stats-polling-interval, like this:

{ "execute": "qom-set",
  "arguments": { "path": "/machine/peripheral-anon/device[1]",
                 "property": "guest-stats-polling-interval", "value": 4 } }

Then the available stats can be retrieved by querying the
guest-stats property. The returned object is a dict containing
all available stats. Example:

{ "execute": "qom-get",
  "arguments": { "path": "/machine/peripheral-anon/device[1]",
  "property": "guest-stats" } }

{
    "return": {
        "stats": {
            "stat-swap-out": 0,
            "stat-free-memory": 844943360,
            "stat-minor-faults": 219028,
            "stat-major-faults": 235,
            "stat-total-memory": 1044406272,
            "stat-swap-in": 0
        },
        "last-update": 1358529861
    }
}

Please, check the next commit for full documentation.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
---
 hw/virtio-balloon.c | 151 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 150 insertions(+), 1 deletion(-)

Am 25.01.13 um 15:14 schrieb Luiz Capitulino:
> The statistics are now available through device properties via a
> polling mechanism. First a client has to enable polling, then it
> can query available stats.
>
> Polling is enabled by setting an update interval (in seconds)
> to a property named guest-stats-polling-interval, like this:
>
> { "execute": "qom-set",
>    "arguments": { "path": "/machine/peripheral-anon/device[1]",
>                   "property": "guest-stats-polling-interval", "value": 4 } }
>
> Then the available stats can be retrieved by querying the
> guest-stats property. The returned object is a dict containing
> all available stats. Example:
>
> { "execute": "qom-get",
>    "arguments": { "path": "/machine/peripheral-anon/device[1]",
>    "property": "guest-stats" } }
>
> {
>      "return": {
>          "stats": {
>              "stat-swap-out": 0,
>              "stat-free-memory": 844943360,
>              "stat-minor-faults": 219028,
>              "stat-major-faults": 235,
>              "stat-total-memory": 1044406272,
>              "stat-swap-in": 0
>          },
>          "last-update": 1358529861
>      }
> }
>
> Please, check the next commit for full documentation.
>
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>   hw/virtio-balloon.c | 151 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 150 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
> index 2520cba..c0a7902 100644
> --- a/hw/virtio-balloon.c
> +++ b/hw/virtio-balloon.c
> @@ -14,6 +14,7 @@
>    */
>
>   #include "qemu/iov.h"
> +#include "qemu/timer.h"
>   #include "qemu-common.h"
>   #include "virtio.h"
>   #include "pc.h"
> @@ -22,6 +23,7 @@
>   #include "virtio-balloon.h"
>   #include "sysemu/kvm.h"
>   #include "exec/address-spaces.h"
> +#include "qapi/visitor.h"
>
>   #if defined(__linux__)
>   #include <sys/mman.h>
> @@ -36,6 +38,9 @@ typedef struct VirtIOBalloon
>       uint64_t stats[VIRTIO_BALLOON_S_NR];
>       VirtQueueElement stats_vq_elem;
>       size_t stats_vq_offset;
> +    QEMUTimer *stats_timer;
> +    int64_t stats_last_update;
> +    int64_t stats_poll_interval;
>       DeviceState *qdev;
>   } VirtIOBalloon;
>
> @@ -53,6 +58,16 @@ static void balloon_page(void *addr, int deflate)
>   #endif
>   }
>
> +static const char *balloon_stat_names[] = {
> +   [VIRTIO_BALLOON_S_SWAP_IN] = "stat-swap-in",
> +   [VIRTIO_BALLOON_S_SWAP_OUT] = "stat-swap-out",
> +   [VIRTIO_BALLOON_S_MAJFLT] = "stat-major-faults",
> +   [VIRTIO_BALLOON_S_MINFLT] = "stat-minor-faults",
> +   [VIRTIO_BALLOON_S_MEMFREE] = "stat-free-memory",
> +   [VIRTIO_BALLOON_S_MEMTOT] = "stat-total-memory",
> +   [VIRTIO_BALLOON_S_NR] = NULL
> +};
> +
>   /*
>    * reset_stats - Mark all items in the stats array as unset
>    *
> @@ -67,6 +82,118 @@ static inline void reset_stats(VirtIOBalloon *dev)
>       for (i = 0; i < VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
>   }
>
> +static bool balloon_stats_supported(const VirtIOBalloon *s)
> +{
> +    return s->vdev.guest_features & (1 << VIRTIO_BALLOON_F_STATS_VQ);
> +}
> +
> +static bool balloon_stats_enabled(const VirtIOBalloon *s)
> +{
> +    return s->stats_poll_interval > 0;
> +}
> +
> +static void balloon_stats_destroy_timer(VirtIOBalloon *s)
> +{
> +    if (balloon_stats_enabled(s)) {
> +        qemu_del_timer(s->stats_timer);
> +        qemu_free_timer(s->stats_timer);
> +        s->stats_timer = NULL;
> +        s->stats_poll_interval = 0;
> +    }
> +}
> +
> +static void balloon_stats_change_timer(VirtIOBalloon *s, int secs)
> +{
> +    qemu_mod_timer(s->stats_timer, qemu_get_clock_ms(vm_clock) + secs * 1000);
> +}
> +
> +static void balloon_stats_poll_cb(void *opaque)
> +{
> +    VirtIOBalloon *s = opaque;
> +
> +    if (!balloon_stats_supported(s)) {
> +        /* re-schedule */
> +        balloon_stats_change_timer(s, s->stats_poll_interval);
> +        return;
> +    }
> +
> +    virtqueue_push(s->svq, &s->stats_vq_elem, s->stats_vq_offset);
> +    virtio_notify(&s->vdev, s->svq);
> +}
> +
> +static void balloon_stats_get_all(Object *obj, struct Visitor *v,
> +                                  void *opaque, const char *name, Error **errp)
> +{
> +    VirtIOBalloon *s = opaque;
> +    int i;
> +
> +    if (!s->stats_last_update) {
> +        error_setg(errp, "guest hasn't updated any stats yet");
> +        return;
> +    }
> +
> +    visit_start_struct(v, NULL, "guest-stats", name, 0, errp);
> +    visit_type_int(v, &s->stats_last_update, "last-update", errp);
> +
> +    visit_start_struct(v, NULL, NULL, "stats", 0, errp);
> +    for (i = 0; i < VIRTIO_BALLOON_S_NR; i++) {
> +        visit_type_int64(v, (int64_t *) &s->stats[i], balloon_stat_names[i],
> +                         errp);
> +    }
> +    visit_end_struct(v, errp);
> +
> +    visit_end_struct(v, errp);
> +}
> +
> +static void balloon_stats_get_poll_interval(Object *obj, struct Visitor *v,
> +                                            void *opaque, const char *name,
> +                                            Error **errp)
> +{
> +    VirtIOBalloon *s = opaque;
> +    visit_type_int(v, &s->stats_poll_interval, name, errp);
> +}
> +
> +static void balloon_stats_set_poll_interval(Object *obj, struct Visitor *v,
> +                                            void *opaque, const char *name,
> +                                            Error **errp)
> +{
> +    VirtIOBalloon *s = opaque;
> +    int64_t value;
> +
> +    visit_type_int(v, &value, name, errp);
> +    if (error_is_set(errp)) {
> +        return;
> +    }
> +
> +    if (value < 0) {
> +        error_setg(errp, "timer value must be greater than zero");
> +        return;
> +    }
> +
> +    if (value == s->stats_poll_interval) {
> +        return;
> +    }
> +
> +    if (value == 0) {
> +        /* timer=0 disables the timer */
> +        balloon_stats_destroy_timer(s);
> +        return;
> +    }
> +
> +    if (balloon_stats_enabled(s)) {
> +        /* timer interval change */
> +        s->stats_poll_interval = value;
> +        balloon_stats_change_timer(s, value);
> +        return;
> +    }
> +
> +    /* create a new timer */
> +    g_assert(s->stats_timer == NULL);
> +    s->stats_timer = qemu_new_timer_ms(vm_clock, balloon_stats_poll_cb, s);
> +    s->stats_poll_interval = value;
> +    balloon_stats_change_timer(s, 0);
> +}
> +
>   static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>   {
>       VirtIOBalloon *s = to_virtio_balloon(vdev);
> @@ -107,9 +234,10 @@ static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
>       VirtQueueElement *elem = &s->stats_vq_elem;
>       VirtIOBalloonStat stat;
>       size_t offset = 0;
> +    qemu_timeval tv;
>
>       if (!virtqueue_pop(vq, elem)) {
> -        return;
> +        goto out;
>       }
>
>       /* Initialize the stats to get rid of any stale values.  This is only
> @@ -128,6 +256,18 @@ static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
>               s->stats[tag] = val;
>       }
>       s->stats_vq_offset = offset;
> +
> +    if (qemu_gettimeofday(&tv) < 0) {
> +        fprintf(stderr, "warning: %s: failed to get time of day\n", __func__);
> +        goto out;
> +    }
> +
> +    s->stats_last_update = tv.tv_sec;
> +
> +out:
> +    if (balloon_stats_enabled(s)) {
> +        balloon_stats_change_timer(s, s->stats_poll_interval);
> +    }
>   }
>
>   static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
> @@ -237,6 +377,14 @@ VirtIODevice *virtio_balloon_init(DeviceState *dev)
>       register_savevm(dev, "virtio-balloon", -1, 1,
>                       virtio_balloon_save, virtio_balloon_load, s);
>
> +    object_property_add(OBJECT(dev), "guest-stats", "guest statistics",
> +                        balloon_stats_get_all, NULL, NULL, s, NULL);
> +
> +    object_property_add(OBJECT(dev), "guest-stats-polling-interval", "int",
> +                        balloon_stats_get_poll_interval,
> +                        balloon_stats_set_poll_interval,
> +                        NULL, s, NULL);
> +
>       return &s->vdev;
>   }
>
> @@ -244,6 +392,7 @@ void virtio_balloon_exit(VirtIODevice *vdev)
>   {
>       VirtIOBalloon *s = DO_UPCAST(VirtIOBalloon, vdev, vdev);
>
> +    balloon_stats_destroy_timer(s);
>       qemu_remove_balloon_handler(s);
>       unregister_savevm(s->qdev, "virtio-balloon", s);
>       virtio_cleanup(vdev);
>

I have a use case where it is not necessary to monitor the guest's 
statistics continuously, i.e. polling-based. However, at some point in 
time I need the information on how much memory is currently used by the 
guest. And that information should be as accurate as possible, hence I 
am not sure if the 1 second granularity is enough for me.

So my question is: Is it planned or already possible to use this new 
interface in an event-based manner? I.e. trigger the collecting of the 
guest's statistics and qeurying the results with the qom interface 
described above?