On Tue, Feb 23, 2016 at 05:59:44PM +0300, Denis V. Lunev wrote:
> From: Igor Redko <red...@virtuozzo.com>
>
> We are making experiments with different autoballooning strategies
> based on the guest behavior. Thus we need to experiment with different
> guest statistics. For now every counter change requires QEMU recompilation
> and dances with Libvirt.
>
> This patch introduces transport for unrecognized counters in virtio-balloon.
> This transport can be used for measuring benefits from using new
> balloon counters, before submitting any patches. Current alternative
> is 'guest-exec' transport which isn't made for such delicate matters
> and can influence test results.
>
> Originally all counters with tag >= VIRTIO_BALLOON_S_NR were ignored.
> Instead of this we keep first (VIRTIO_BALLOON_S_NR + 32) counters from the
> queue and pass unrecognized ones with the following names: 'x-stat-XXXX',
> where XXXX is a tag number in hex. Defined counters are reported with their
> regular names.
>
> Signed-off-by: Igor Redko <red...@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <d...@openvz.org>
> CC: Michael S. Tsirkin <m...@redhat.com>
This seems to open the ABI to abuse.
Seems like a reasonable way to experiment though.
How about adding this within #if 0 statements?
You can uncomment them for debugging ...
> ---
> hw/virtio/virtio-balloon.c | 30 ++++++++++++++++++++++++------
> include/hw/virtio/virtio-balloon.h | 3 ++-
> 2 files changed, 26 insertions(+), 7 deletions(-)
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index a382f43..1740293 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -66,8 +66,7 @@ static const char *balloon_stat_names[] = {
> */
> static inline void reset_stats(VirtIOBalloon *dev)
> {
> - int i;
> - for (i = 0; i < VIRTIO_BALLOON_S_NR; dev->stats[i++] = -1);
> + dev->stats_cnt = 0;
> }
>
> static bool balloon_stats_supported(const VirtIOBalloon *s)
> @@ -133,12 +132,20 @@ static void balloon_stats_get_all(Object *obj, Visitor
> *v, const char *name,
> if (err) {
> goto out_end;
> }
> - for (i = 0; i < VIRTIO_BALLOON_S_NR; i++) {
> - visit_type_uint64(v, balloon_stat_names[i], &s->stats[i], &err);
> + for (i = 0; i < s->stats_cnt; i++) {
> + if (s->stats[i].tag < VIRTIO_BALLOON_S_NR) {
> + visit_type_uint64(v, balloon_stat_names[s->stats[i].tag],
> + &s->stats[i].val, &err);
> + } else {
> + gchar *str = g_strdup_printf("x-stat-%04x", s->stats[i].tag);
> + visit_type_uint64(v, str, &s->stats[i].val, &err);
> + g_free(str);
> + }
> if (err) {
> break;
> }
> }
> +
> error_propagate(errp, err);
> err = NULL;
> visit_end_struct(v, &err);
> @@ -273,10 +280,21 @@ static void virtio_balloon_receive_stats(VirtIODevice
> *vdev, VirtQueue *vq)
> == sizeof(stat)) {
> uint16_t tag = virtio_tswap16(vdev, stat.tag);
> uint64_t val = virtio_tswap64(vdev, stat.val);
> + int i;
>
> offset += sizeof(stat);
> - if (tag < VIRTIO_BALLOON_S_NR)
> - s->stats[tag] = val;
> + for (i = 0; i < s->stats_cnt; i++) {
> + if (s->stats[i].tag == tag) {
> + break;
> + }
> + }
> + if (i < ARRAY_SIZE(s->stats)) {
> + s->stats[i].tag = tag;
> + s->stats[i].val = val;
> + if (s->stats_cnt <= i) {
> + s->stats_cnt = i + 1;
> + }
> + }
> }
> s->stats_vq_offset = offset;
>
> diff --git a/include/hw/virtio/virtio-balloon.h
> b/include/hw/virtio/virtio-balloon.h
> index 35f62ac..5c8730e 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -36,7 +36,8 @@ typedef struct VirtIOBalloon {
> VirtQueue *ivq, *dvq, *svq;
> uint32_t num_pages;
> uint32_t actual;
> - uint64_t stats[VIRTIO_BALLOON_S_NR];
> + VirtIOBalloonStatModern stats[VIRTIO_BALLOON_S_NR + 32];
> + uint16_t stats_cnt;
> VirtQueueElement *stats_vq_elem;
> size_t stats_vq_offset;
> QEMUTimer *stats_timer;
> --
> 2.1.4
