Re: [Qemu-devel] [RFC 2/3] virtio-balloon: re-enable balloon stats

[mdroth <mdroth@linux.vnet.ibm.com>]

On Tue, Dec 04, 2012 at 01:04:47PM -0200, Luiz Capitulino wrote:
> The statistics are now available through device properties via a
> polling mechanism. First, a client has to enable polling, then it
> can query the stats.
> 
> The following control properties are introduced:
> 
>  o stats-polling-interval: a value greater than zero enables polling
>    in the specified interval (in seconds). When value equals zero,
>    polling is disabled. If polling is already enabled and a value
>    greater than zero is written, the polling interval time is changed
> 
>  o stats-last-update: last stats update timestamp, in seconds.
> 
> The following stats properties are introduced:
> 
>  o stat-swap-in
>  o stat-swap-out
>  o stat-major-faults
>  o stat-minor-faults
>  o stat-free-memory
>  o stat-total-memory
> 
> All values are in bytes. A value of -1 means that the statistic isn't
> available right now.
> 
> FIXME: Can balloon_stats_poll_cb(), balloon_stats_set_poll_interval(),
>        virtio_balloon_handle_output() can run in parallel?
> 
> XXX: Should we return an error instead of -1? Might require a specific
>      error. Although this is not exactly a failure...
> 
> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> ---
> 
> NOTE: Anthony suggested having a bool to enable/disable polling, but I prefer
>       to let the client specify the polling interval. I can revisit this,
> 	  though.
> 
>  hw/virtio-balloon.c | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 155 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
> index 4398025..06af18f 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 "qemu-timer.h"
> +#include "qapi/qapi-visit-core.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 +82,119 @@ 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_disable_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;
> +
> +    virtqueue_push(s->svq, &s->stats_vq_elem, s->stats_vq_offset);
> +    virtio_notify(&s->vdev, s->svq);

I think we'll want to add some logic to avoid the potential for
re-pushing an elem we've already processed, as I think that violates the
virtio spec. In the past the monitor blocked us from doing this but with
timer-driven requests I think it's a possibility now.

But the general approach seems sane to me and the code looks to
be in decent shape.

> -- 
> 1.8.0
> 
>