On Mon, Dec 08, 2025 at 08:09:51PM +0800, Chuang Xu wrote:
> From: xuchuangxclwt <[email protected]>
>
> Although logs can now be shared among multiple vhost devices,
> live migration still performs repeated vhost_log_sync for each
> vhost device during bitmap_sync, which increases the time required
> for bitmap_sync and makes it more difficult for dirty pages to converge.
>
> Attempt to eliminate these duplicate sync.
>
> Signed-off-by: Chuang Xu <[email protected]>
It looks reasonable from migration POV, but I don't know the details.
Please remember to copy Jason (I added for this email) when repost.
Thanks,
> ---
> hw/virtio/vhost.c | 30 ++++++++++++++++++++++--------
> include/hw/virtio/vhost.h | 1 +
> 2 files changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 266a11514a..d397ca327f 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -268,14 +268,6 @@ static int vhost_sync_dirty_bitmap(struct vhost_dev *dev,
> return 0;
> }
>
> -static void vhost_log_sync(MemoryListener *listener,
> - MemoryRegionSection *section)
> -{
> - struct vhost_dev *dev = container_of(listener, struct vhost_dev,
> - memory_listener);
> - vhost_sync_dirty_bitmap(dev, section, 0x0, ~0x0ULL);
> -}
> -
> static void vhost_log_sync_range(struct vhost_dev *dev,
> hwaddr first, hwaddr last)
> {
> @@ -287,6 +279,27 @@ static void vhost_log_sync_range(struct vhost_dev *dev,
> }
> }
>
> +static void vhost_log_sync(MemoryListener *listener,
> + MemoryRegionSection *section)
> +{
> + struct vhost_dev *dev = container_of(listener, struct vhost_dev,
> + memory_listener);
> + struct vhost_log *log = dev->log;
> +
> + if (log && log->refcnt > 1) {
> + /*
> + * When multiple devices use same log, we implement the logic of
> + * vhost_log_sync just like what we do in vhost_log_put.
> + */
> + log->sync_cnt = (log->sync_cnt + 1) % log->refcnt;
> + if (!log->sync_cnt) {
> + vhost_log_sync_range(dev, 0, dev->log_size * VHOST_LOG_CHUNK -
> 1);
> + }
> + } else {
> + vhost_sync_dirty_bitmap(dev, section, 0x0, ~0x0ULL);
> + }
> +}
> +
> static uint64_t vhost_get_log_size(struct vhost_dev *dev)
> {
> uint64_t log_size = 0;
> @@ -383,6 +396,7 @@ static struct vhost_log *vhost_log_get(VhostBackendType
> backend_type,
> ++log->refcnt;
> }
>
> + log->sync_cnt = 0;
> return log;
> }
>
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 08bbb4dfe9..43bf1c2150 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -50,6 +50,7 @@ typedef unsigned long vhost_log_chunk_t;
> struct vhost_log {
> unsigned long long size;
> int refcnt;
> + int sync_cnt;
> int fd;
> vhost_log_chunk_t *log;
> };
> --
> 2.20.1
>
--
Peter Xu
