Re: [Qemu-devel] [PATCH 6/6] qmp: add balloon-get-memory-stats & event

[Adam Litke <agl@us.ibm.com>]

On Wed, Feb 08, 2012 at 06:30:40PM -0200, Luiz Capitulino wrote:
> This commit adds a QMP API for the guest provided memory statistics
> (long disabled by commit 07b0403dfc2b2ac179ae5b48105096cc2d03375a).
> 
> The approach taken by the original commit
> (625a5befc2e3200b396594f002218d235e375da5) was to extend the
> query-balloon command. It introduced a severe bug though: query-balloon
> would hang if the guest didn't respond.
> 
> The approach taken by this commit is asynchronous and thus avoids
> any QMP hangs.
> 
> First, a client has to issue the balloon-get-memory-stats command.
> That command gets the process started by only sending a request to
> the guest, it doesn't block. When the memory stats are made available
> by the guest, they are returned to the client as an QMP event.
> 
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> ---
>  QMP/qmp-events.txt  |   36 ++++++++++++++++++++++++
>  balloon.c           |   30 +++++++++++++++++++-
>  balloon.h           |    4 ++-
>  hw/virtio-balloon.c |   76 ++++++++++++++++++++++++++++++++++-----------------
>  monitor.c           |    2 +
>  monitor.h           |    1 +
>  qapi-schema.json    |   21 ++++++++++++++
>  qmp-commands.hx     |    5 +++
>  8 files changed, 147 insertions(+), 28 deletions(-)
> 
> diff --git a/QMP/qmp-events.txt b/QMP/qmp-events.txt
> index 06cb404..b34b289 100644
> --- a/QMP/qmp-events.txt
> +++ b/QMP/qmp-events.txt
> @@ -1,6 +1,42 @@
>                     QEMU Monitor Protocol Events
>                     ============================
> 
> +BALLOON_MEMORY_STATS
> +--------------------
> +
> +Emitted when memory statistics information is made available by the guest.
> +
> +Data:
> +
> +- "memory-swapped-in": number of pages swapped in within the guest
> +  (json-int, optional)
> +- "memory-swapped-out": number of pages swapped out within the guest
> +  (json-int, optional)

These are in units of pages where memory-total and memory-free are in bytes.
Maybe it makes sense to name these "memory-pages-swapped-in/out" to avoid
confusion.  Yes it makes them longer, but I can imagine all of the questions in
the future when users don't expect the units to be in pages.

> +- "major-page-faults": number of major page faults within the guest
> +  (json-int, optional)
> +- "minor-page-faults": number of minor page faults within the guest
> +  (json-int, optional)
> +- "memory-free": amount of memory (in bytes) free in the guest
> +  (json-int, optional)
> +- "memory-total": amount of memory (in bytes) visible to the guest
> +  (json-int, optional)
> +
> +Example:
> +
> +{ "event": "BALLOON_MEMORY_STATS",
> +    "data": { "memory-free": 847941632,
> +              "major-page-faults": 225,
> +              "memory-swapped-in": 0,
> +              "minor-page-faults": 222317,
> +              "memory-total": 1045516288,
> +              "memory-swapped-out": 0 },
> +    "timestamp": { "seconds": 1265044230, "microseconds": 450486 } }
> +
> +Notes: o The balloon-get-memory-stats command must be issued first, to tell
> +         the guest to make the memory statistics available.
> +       o The event may not contain all data members when emitted
> +
> +
>  BLOCK_IO_ERROR
>  --------------
> 
> diff --git a/balloon.c b/balloon.c
> index d340ae3..1c1a3c1 100644
> --- a/balloon.c
> +++ b/balloon.c
> @@ -33,12 +33,15 @@
> 
>  static QEMUBalloonEvent *balloon_event_fn;
>  static QEMUBalloonInfo *balloon_info_fn;
> +static QEMUBalloonStats *balloon_stats_fn;
>  static void *balloon_opaque;
> 
>  int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
> -                             QEMUBalloonInfo *info_func, void *opaque)
> +                             QEMUBalloonInfo *info_func,
> +                             QEMUBalloonStats *stats_func, void *opaque)
>  {
> -    if (balloon_event_fn || balloon_info_fn || balloon_opaque) {
> +    if (balloon_event_fn || balloon_info_fn || balloon_stats_fn ||
> +        balloon_opaque) {
>          /* We're already registered one balloon handler.  How many can
>           * a guest really have?
>           */
> @@ -47,6 +50,7 @@ int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
>      }
>      balloon_event_fn = event_func;
>      balloon_info_fn = info_func;
> +    balloon_stats_fn = stats_func;
>      balloon_opaque = opaque;
>      return 0;
>  }
> @@ -58,6 +62,7 @@ void qemu_remove_balloon_handler(void *opaque)
>      }
>      balloon_event_fn = NULL;
>      balloon_info_fn = NULL;
> +    balloon_stats_fn = NULL;
>      balloon_opaque = NULL;
>  }
> 
> @@ -80,6 +85,15 @@ static int qemu_balloon_info(BalloonInfo *info)
>      return 1;
>  }
> 
> +static int qemu_balloon_stats(void)
> +{
> +    if (!balloon_stats_fn) {
> +        return 0;
> +    }
> +    balloon_stats_fn(balloon_opaque);
> +    return 1;
> +}
> +
>  static bool check_kvm_sync_mmu(Error **errp)
>  {
>      if (kvm_enabled() && !kvm_has_sync_mmu()) {
> @@ -89,6 +103,18 @@ static bool check_kvm_sync_mmu(Error **errp)
>      return true;
>  }
> 
> +void qmp_balloon_get_memory_stats(Error **errp)
> +{
> +    if (!check_kvm_sync_mmu(errp)) {
> +        return;
> +    }
> +
> +    if (qemu_balloon_stats() == 0) {
> +        error_set(errp, QERR_DEVICE_NOT_ACTIVE, "balloon");
> +        return;
> +    }
> +}
> +
>  BalloonInfo *qmp_query_balloon(Error **errp)
>  {
>      BalloonInfo *info;
> diff --git a/balloon.h b/balloon.h
> index a539354..509e477 100644
> --- a/balloon.h
> +++ b/balloon.h
> @@ -18,9 +18,11 @@
> 
>  typedef void (QEMUBalloonEvent)(void *opaque, ram_addr_t target);
>  typedef void (QEMUBalloonInfo)(void *opaque, BalloonInfo *info);
> +typedef void (QEMUBalloonStats)(void *opaque);
> 
>  int qemu_add_balloon_handler(QEMUBalloonEvent *event_func,
> -			     QEMUBalloonInfo *info_func, void *opaque);
> +			     QEMUBalloonInfo *info_func, QEMUBalloonStats *stats_func,
> +                 void *opaque);
>  void qemu_remove_balloon_handler(void *opaque);
> 
>  #endif
> diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
> index 4307f4c..8bc842c 100644
> --- a/hw/virtio-balloon.c
> +++ b/hw/virtio-balloon.c
> @@ -22,6 +22,8 @@
>  #include "virtio-balloon.h"
>  #include "kvm.h"
>  #include "exec-memory.h"
> +#include "monitor.h"
> +#include "qemu-objects.h"
> 
>  #if defined(__linux__)
>  #include <sys/mman.h>
> @@ -34,6 +36,7 @@ typedef struct VirtIOBalloon
>      uint32_t num_pages;
>      uint32_t actual;
>      uint64_t stats[VIRTIO_BALLOON_S_NR];
> +    bool stats_requested;
>      VirtQueueElement stats_vq_elem;
>      size_t stats_vq_offset;
>      DeviceState *qdev;
> @@ -56,12 +59,10 @@ static void balloon_page(void *addr, int deflate)
>  /*
>   * reset_stats - Mark all items in the stats array as unset
>   *
> - * This function needs to be called at device intialization and before
> - * before updating to a set of newly-generated stats.  This will ensure that no
> - * stale values stick around in case the guest reports a subset of the supported
> - * statistics.
> + * This function ensures that no stale values stick around in case the guest
> + * reports a subset of the supported statistics.
>   */
> -static inline void reset_stats(VirtIOBalloon *dev)
> +static void reset_stats(VirtIOBalloon *dev)
>  {
>      int i;
>      for (i = 0; i < VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
> @@ -101,6 +102,38 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, VirtQueue *vq)
>      }
>  }
> 
> +static void emit_qmp_balloon_event(const VirtIOBalloon *dev)
> +{
> +    int i;
> +    QDict *stats;
> +    const struct stats_strings {
> +        int stat_idx;
> +        const char *stat_name;
> +    } stats_strings[] = {
> +        { VIRTIO_BALLOON_S_SWAP_IN, "memory-swapped-in" },
> +        { VIRTIO_BALLOON_S_SWAP_OUT, "memory-swapped-out" },
> +        { VIRTIO_BALLOON_S_MAJFLT, "major-page-faults" },
> +        { VIRTIO_BALLOON_S_MINFLT, "minor-page-faults" },
> +        { VIRTIO_BALLOON_S_MEMFREE, "memory-free" },
> +        { VIRTIO_BALLOON_S_MEMTOT, "memory-total" },
> +        { 0, NULL },
> +    };
> +
> +    stats = qdict_new();
> +    for (i = 0; stats_strings[i].stat_name != NULL; i++) {
> +        if (dev->stats[i] != -1) {
> +            qdict_put(stats, stats_strings[i].stat_name,
> +                      qint_from_int(dev->stats[i]));
> +        }
> +    }
> +
> +    if (qdict_size(stats) > 0) {
> +        monitor_protocol_event(QEVENT_BALLOON_STATS, QOBJECT(stats));
> +    }
> +
> +    QDECREF(stats);
> +}
> +
>  static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
>  {
>      VirtIOBalloon *s = DO_UPCAST(VirtIOBalloon, vdev, vdev);
> @@ -108,7 +141,7 @@ static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
>      VirtIOBalloonStat stat;
>      size_t offset = 0;
> 
> -    if (!virtqueue_pop(vq, elem)) {
> +    if (!virtqueue_pop(vq, elem) || !s->stats_requested) {
>          return;
>      }
> 
> @@ -128,6 +161,9 @@ static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
>              s->stats[tag] = val;
>      }
>      s->stats_vq_offset = offset;
> +    s->stats_requested = false;
> +
> +    emit_qmp_balloon_event(s);
>  }
> 
>  static void virtio_balloon_get_config(VirtIODevice *vdev, uint8_t *config_data)
> @@ -156,31 +192,21 @@ static uint32_t virtio_balloon_get_features(VirtIODevice *vdev, uint32_t f)
>      return f;
>  }
> 
> -static void virtio_balloon_info(void *opaque, BalloonInfo *info)
> +static void virtio_balloon_stats(void *opaque)
>  {
>      VirtIOBalloon *dev = opaque;
> 
> -#if 0
> -    /* Disable guest-provided stats for now. For more details please check:
> -     * https://bugzilla.redhat.com/show_bug.cgi?id=623903
> -     *
> -     * If you do enable it (which is probably not going to happen as we
> -     * need a new command for it), remember that you also need to fill the
> -     * appropriate members of the BalloonInfo structure so that the stats
> -     * are returned to the client.
> -     */
>      if (dev->vdev.guest_features & (1 << VIRTIO_BALLOON_F_STATS_VQ)) {
> +        dev->stats_requested = true;
>          virtqueue_push(dev->svq, &dev->stats_vq_elem, dev->stats_vq_offset);
>          virtio_notify(&dev->vdev, dev->svq);
>          return;
>      }
> -#endif
> -
> -    /* Stats are not supported.  Clear out any stale values that might
> -     * have been set by a more featureful guest kernel.
> -     */
> -    reset_stats(dev);
> +}
> 
> +static void virtio_balloon_info(void *opaque, BalloonInfo *info)
> +{
> +    VirtIOBalloon *dev = opaque;
>      info->actual = ram_size - ((uint64_t) dev->actual <<
>                                 VIRTIO_BALLOON_PFN_SHIFT);
>  }
> @@ -236,18 +262,18 @@ VirtIODevice *virtio_balloon_init(DeviceState *dev)
>      s->vdev.get_features = virtio_balloon_get_features;
> 
>      ret = qemu_add_balloon_handler(virtio_balloon_to_target,
> -                                   virtio_balloon_info, s);
> +                                   virtio_balloon_info,
> +                                   virtio_balloon_stats, s);
>      if (ret < 0) {
>          virtio_cleanup(&s->vdev);
>          return NULL;
>      }
> 
> +    s->stats_requested = false;
>      s->ivq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
>      s->dvq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
>      s->svq = virtio_add_queue(&s->vdev, 128, virtio_balloon_receive_stats);
> 
> -    reset_stats(s);
> -
>      s->qdev = dev;
>      register_savevm(dev, "virtio-balloon", -1, 1,
>                      virtio_balloon_save, virtio_balloon_load, s);
> diff --git a/monitor.c b/monitor.c
> index aadbdcb..868f2a0 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -484,6 +484,8 @@ void monitor_protocol_event(MonitorEvent event, QObject *data)
>              break;
>          case QEVENT_BLOCK_JOB_CANCELLED:
>              event_name = "BLOCK_JOB_CANCELLED";
> +        case QEVENT_BALLOON_STATS:
> +            event_name = "BALLOON_MEMORY_STATS";
>              break;
>          default:
>              abort();
> diff --git a/monitor.h b/monitor.h
> index b72ea07..76e26c7 100644
> --- a/monitor.h
> +++ b/monitor.h
> @@ -38,6 +38,7 @@ typedef enum MonitorEvent {
>      QEVENT_SPICE_DISCONNECTED,
>      QEVENT_BLOCK_JOB_COMPLETED,
>      QEVENT_BLOCK_JOB_CANCELLED,
> +    QEVENT_BALLOON_STATS,
>      QEVENT_MAX,
>  } MonitorEvent;
> 
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 24a42e3..c4d8d0c 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1563,3 +1563,24 @@
>  { 'command': 'qom-list-types',
>    'data': { '*implements': 'str', '*abstract': 'bool' },
>    'returns': [ 'ObjectTypeInfo' ] }
> +
> +##
> +# @balloon-get-memory-stats
> +#
> +# Ask the guest's balloon driver for guest memory statistics.
> +#
> +# This command will only get the process started and will return immediately.
> +# The BALLOON_MEMORY_STATS event will be emitted when the statistics
> +# information is returned by the guest.
> +#
> +# Returns: nothing on success
> +#          If the balloon driver is enabled but not functional because the KVM
> +#          kernel module cannot support it, KvmMissingCap
> +#          If no balloon device is present, DeviceNotActive
> +#
> +# Notes: There's no guarantees the guest will ever respond, thus the
> +#        BALLOON_MEMORY_STATS event may never be emitted.
> +#
> +# Since: 1.1
> +##
> +{ 'command': 'balloon-get-memory-stats' }
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index b5e2ab8..52c1fc3 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -2047,3 +2047,8 @@ EQMP
>          .args_type  = "implements:s?,abstract:b?",
>          .mhandler.cmd_new = qmp_marshal_input_qom_list_types,
>      },
> +    {
> +        .name       = "balloon-get-memory-stats",
> +        .args_type  = "",
> +        .mhandler.cmd_new = qmp_marshal_input_balloon_get_memory_stats,
> +    },
> -- 
> 1.7.9.111.gf3fb0.dirty
> 

-- 
Adam Litke <agl@us.ibm.com>
IBM Linux Technology Center