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

[Luiz Capitulino <lcapitulino@redhat.com>]

On Thu, 6 Dec 2012 11:03:21 -0600
mdroth <mdroth@linux.vnet.ibm.com> wrote:

> 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.

I'll check that, thanks for the feedback Mike.

> 
> But the general approach seems sane to me and the code looks to
> be in decent shape.
> 
> > -- 
> > 1.8.0
> > 
> > 
>