[dpdk-dev] vhost: reserve some spaces for virtio_net and vhost_virtqueue struct
Commit Message
So that we will not break ABI in future extension by adding few more
fields.
Struct vhost_virtqueue is reserved with 16 qwords (the later vhost-live
migration support would at least consume 3 of them), and struct virtio_net
is reserved with a bit more, 64 qwords, as there is only one instance for
a virtio nic instance.
Note that both reservation are not placed at the end of the struct, but
instead before the last field, since both the last field at the two struct
take a lot spaces. Putting the reservation after it would divide those
reserved fields to another cacheline. (we might need fix them in future, btw)
CC: Panu Matilainen <pmatilai@redhat.com>
CC: Thomas Monjalon <thomas.monjalon@6wind.com>
CC: Michael S. Tsirkin <mst@redhat.com>
CC: Victor Kaplansky <vkaplans@redhat.com>
Suggested-by: Panu Matilainen <pmatilai@redhat.com>
Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
---
Is the reservation a bit too large? :)
---
lib/librte_vhost/rte_virtio_net.h | 2 ++
1 file changed, 2 insertions(+)
Comments
2015-12-03 10:27, Yuanhan Liu:
> So that we will not break ABI in future extension by adding few more
> fields.
>
> Struct vhost_virtqueue is reserved with 16 qwords (the later vhost-live
> migration support would at least consume 3 of them), and struct virtio_net
> is reserved with a bit more, 64 qwords, as there is only one instance for
> a virtio nic instance.
>
> Note that both reservation are not placed at the end of the struct, but
> instead before the last field, since both the last field at the two struct
> take a lot spaces. Putting the reservation after it would divide those
> reserved fields to another cacheline. (we might need fix them in future, btw)
>
> CC: Panu Matilainen <pmatilai@redhat.com>
> CC: Thomas Monjalon <thomas.monjalon@6wind.com>
> CC: Michael S. Tsirkin <mst@redhat.com>
> CC: Victor Kaplansky <vkaplans@redhat.com>
> Suggested-by: Panu Matilainen <pmatilai@redhat.com>
> Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> ---
>
> Is the reservation a bit too large? :)
You are maintainer in this area.
Applied, thanks
@@ -90,6 +90,7 @@ struct vhost_virtqueue {
int callfd; /**< Used to notify the guest (trigger interrupt). */
int kickfd; /**< Currently unused as polling mode is enabled. */
int enabled;
+ uint64_t reserved[16]; /**< Reserve some spaces for future extension. */
struct buf_vector buf_vec[BUF_VECTOR_MAX]; /**< for scatter RX. */
} __rte_cache_aligned;
@@ -128,6 +129,7 @@ struct virtio_net {
char ifname[IF_NAME_SZ]; /**< Name of the tap device or socket path. */
uint32_t virt_qp_nb; /**< number of queue pair we have allocated */
void *priv; /**< private context */
+ uint64_t reserved[64]; /**< Reserve some spaces for future extension. */
struct vhost_virtqueue *virtqueue[VHOST_MAX_QUEUE_PAIRS * 2]; /**< Contains all virtqueue information. */
} __rte_cache_aligned;