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/qemu/include/hw/virtio/
H A Dvhost.h309750fad51f17d1ec6195c5d8ad7d741596ddb6 Thu Jun 04 09:28:46 UTC 2015 Jason Wang <jasowang@redhat.com> vhost: logs sharing

Currently we allocate one vhost log per vhost device. This is sub
optimal when:

- Guest has several device with vhost as backend
- Guest has multiqueue devices

In the above cases, we can avoid the memory allocation by sharing a
single vhost log among all the vhost devices. This is done through:

- Introducing a new vhost_log structure with refcnt inside.
- Using a global pointer to vhost_log structure that will be used. And
introduce helper to get the log with expected log size and helper to
- drop the refcnt to the old log.
- Each vhost device still keep track of a pointer to the log that was
used.

With above, if no resize happens, all vhost device will share a single
vhost log. During resize, a new vhost_log structure will be allocated
and made for the global pointer. And each vhost devices will drop the
refcnt to the old log.

Tested by doing scp during migration for a 2 queues virtio-net-pci.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
/qemu/hw/virtio/
H A Dvhost.c309750fad51f17d1ec6195c5d8ad7d741596ddb6 Thu Jun 04 09:28:46 UTC 2015 Jason Wang <jasowang@redhat.com> vhost: logs sharing

Currently we allocate one vhost log per vhost device. This is sub
optimal when:

- Guest has several device with vhost as backend
- Guest has multiqueue devices

In the above cases, we can avoid the memory allocation by sharing a
single vhost log among all the vhost devices. This is done through:

- Introducing a new vhost_log structure with refcnt inside.
- Using a global pointer to vhost_log structure that will be used. And
introduce helper to get the log with expected log size and helper to
- drop the refcnt to the old log.
- Each vhost device still keep track of a pointer to the log that was
used.

With above, if no resize happens, all vhost device will share a single
vhost log. During resize, a new vhost_log structure will be allocated
and made for the global pointer. And each vhost devices will drop the
refcnt to the old log.

Tested by doing scp during migration for a 2 queues virtio-net-pci.

Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>