On Wed, Feb 14, 2024 at 2:02 PM Si-Wei Liu <si-wei....@oracle.com> wrote:
>
> On setups with one or more virtio-net devices with vhost on,
> dirty tracking iteration increases cost the bigger the number
> amount of queues are set up e.g. on idle guests migration the
> following is observed with virtio-net with vhost=on:
>
> 48 queues -> 78.11% [.] vhost_dev_sync_region.isra.13
> 8 queues -> 40.50% [.] vhost_dev_sync_region.isra.13
> 1 queue -> 6.89% [.] vhost_dev_sync_region.isra.13
> 2 devices, 1 queue -> 18.60% [.] vhost_dev_sync_region.isra.14
>
I think the after benchmark should also be included.
> With high memory rates the symptom is lack of convergence as soon
> as it has a vhost device with a sufficiently high number of queues,
> the sufficient number of vhost devices.
>
> On every migration iteration (every 100msecs) it will redundantly
> query the *shared log* the number of queues configured with vhost
> that exist in the guest. For the virtqueue data, this is necessary,
> but not for the memory sections which are the same. So
> essentially we end up scanning the dirty log too often.
>
> To fix that, select a vhost device responsible for scanning the
> log with regards to memory sections dirty tracking. It is selected
> when we enable the logger (during migration) and cleared when we
> disable the logger. If the vhost logger device goes away for some
> reason, the logger will be re-selected from the rest of vhost
> devices.
>
> Co-developed-by: Joao Martins <joao.m.mart...@oracle.com>
> Signed-off-by: Joao Martins <joao.m.mart...@oracle.com>
> Signed-off-by: Si-Wei Liu <si-wei....@oracle.com>
> ---
> hw/virtio/vhost.c | 75
> +++++++++++++++++++++++++++++++++++++++++++----
> include/hw/virtio/vhost.h | 1 +
> 2 files changed, 70 insertions(+), 6 deletions(-)
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index ef6d9b5..997d560 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -45,6 +45,9 @@
>
> static struct vhost_log *vhost_log[VHOST_BACKEND_TYPE_MAX];
> static struct vhost_log *vhost_log_shm[VHOST_BACKEND_TYPE_MAX];
> +static struct vhost_dev *vhost_mem_logger[VHOST_BACKEND_TYPE_MAX];
> +static QLIST_HEAD(, vhost_dev) vhost_mlog_devices =
> + QLIST_HEAD_INITIALIZER(vhost_mlog_devices);
>
> /* Memslots used by backends that support private memslots (without an fd).
> */
> static unsigned int used_memslots;
> @@ -149,6 +152,53 @@ bool vhost_dev_has_iommu(struct vhost_dev *dev)
> }
> }
>
> +static bool vhost_log_dev_enabled(struct vhost_dev *dev)
"Enabled" sounds misleading to me. Maybe vhost_dev_should_log? More
suggestions below.
> +{
> + assert(dev->vhost_ops);
> + assert(dev->vhost_ops->backend_type > VHOST_BACKEND_TYPE_NONE);
> + assert(dev->vhost_ops->backend_type < VHOST_BACKEND_TYPE_MAX);
> +
> + return dev == vhost_mem_logger[dev->vhost_ops->backend_type];
> +}
> +
> +static void vhost_mlog_set_dev(struct vhost_dev *hdev, bool enable)
> +{
> + struct vhost_dev *logdev = NULL;
> + VhostBackendType backend_type;
> + bool reelect = false;
> +
> + assert(hdev->vhost_ops);
> + assert(hdev->vhost_ops->backend_type > VHOST_BACKEND_TYPE_NONE);
> + assert(hdev->vhost_ops->backend_type < VHOST_BACKEND_TYPE_MAX);
> +
> + backend_type = hdev->vhost_ops->backend_type;
> +
> + if (enable && !QLIST_IS_INSERTED(hdev, logdev_entry)) {
> + reelect = !vhost_mem_logger[backend_type];
> + QLIST_INSERT_HEAD(&vhost_mlog_devices, hdev, logdev_entry);
> + } else if (!enable && QLIST_IS_INSERTED(hdev, logdev_entry)) {
> + reelect = vhost_mem_logger[backend_type] == hdev;
> + QLIST_REMOVE(hdev, logdev_entry);
> + }
> +
> + if (!reelect)
> + return;
> +
> + QLIST_FOREACH(hdev, &vhost_mlog_devices, logdev_entry) {
> + if (!hdev->vhost_ops ||
> + hdev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_NONE ||
> + hdev->vhost_ops->backend_type >= VHOST_BACKEND_TYPE_MAX)
Aren't comparisons with ops->backend_type already contained in the
following "hdev->vhost_ops->backend_type == backend_type" ?
> + continue;
> +
> + if (hdev->vhost_ops->backend_type == backend_type) {
> + logdev = hdev;
> + break;
> + }
Why not use VHOST_BACKEND_TYPE_MAX QLISTs, and then simply check if
*dev is the head at vhost_log_dev_enabled?
That way we can remove this foreach and vhost_log_dev_enabled
entirely, as the check is simpler. I think it could even remove this
function entirely and inline QLIST_INSERT / QLIST_REMOVE at callers.
What do you think?
Thanks!
> + }
> +
> + vhost_mem_logger[backend_type] = logdev;
> +}
> +
> static int vhost_sync_dirty_bitmap(struct vhost_dev *dev,
> MemoryRegionSection *section,
> hwaddr first,
> @@ -166,12 +216,14 @@ static int vhost_sync_dirty_bitmap(struct vhost_dev
> *dev,
> start_addr = MAX(first, start_addr);
> end_addr = MIN(last, end_addr);
>
> - for (i = 0; i < dev->mem->nregions; ++i) {
> - struct vhost_memory_region *reg = dev->mem->regions + i;
> - vhost_dev_sync_region(dev, section, start_addr, end_addr,
> - reg->guest_phys_addr,
> - range_get_last(reg->guest_phys_addr,
> - reg->memory_size));
> + if (vhost_log_dev_enabled(dev)) {
> + for (i = 0; i < dev->mem->nregions; ++i) {
> + struct vhost_memory_region *reg = dev->mem->regions + i;
> + vhost_dev_sync_region(dev, section, start_addr, end_addr,
> + reg->guest_phys_addr,
> + range_get_last(reg->guest_phys_addr,
> + reg->memory_size));
> + }
> }
> for (i = 0; i < dev->nvqs; ++i) {
> struct vhost_virtqueue *vq = dev->vqs + i;
> @@ -382,6 +434,7 @@ static void vhost_log_put(struct vhost_dev *dev, bool
> sync)
> g_free(log);
> }
>
> + vhost_mlog_set_dev(dev, false);
> dev->log = NULL;
> dev->log_size = 0;
> }
> @@ -997,6 +1050,15 @@ static int vhost_dev_set_log(struct vhost_dev *dev,
> bool enable_log)
> goto err_vq;
> }
> }
> +
> + /*
> + * At log start we select our vhost_device logger that will scan the
> + * memory sections and skip for the others. This is possible because
> + * the log is shared amongst all vhost devices for a given type of
> + * backend.
> + */
> + vhost_mlog_set_dev(dev, enable_log);
> +
> return 0;
> err_vq:
> for (; i >= 0; --i) {
> @@ -2072,6 +2134,7 @@ int vhost_dev_start(struct vhost_dev *hdev,
> VirtIODevice *vdev, bool vrings)
> VHOST_OPS_DEBUG(r, "vhost_set_log_base failed");
> goto fail_log;
> }
> + vhost_mlog_set_dev(hdev, true);
> }
> if (vrings) {
> r = vhost_dev_set_vring_enable(hdev, true);
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 0247778..d75faf4 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -129,6 +129,7 @@ struct vhost_dev {
> void *opaque;
> struct vhost_log *log;
> QLIST_ENTRY(vhost_dev) entry;
> + QLIST_ENTRY(vhost_dev) logdev_entry;
> QLIST_HEAD(, vhost_iommu) iommu_list;
> IOMMUNotifier n;
> const VhostDevConfigOps *config_ops;
> --
> 1.8.3.1
>
>
