hw/net/virtio-net: skip automatic zero-init of large arrays

The 'virtio_net_receive_rcu' method has three arrays with
VIRTQUEUE_MAX_SIZE elements, which are apprixmately 32k in
size used for copying data between guest and host. Skip the
automatic zero-init of these arrays to eliminate the
performance overhead in the I/O hot path.

The three arrays will be selectively initialized as required
when processing network buffers.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 20250610123709.835102-22-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 221252e00a50a46033d7ec8d18936e7c8196a6ca..eb93607b8c76c55f59c9c48999ec898f05817357 100644 (file)
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -1911,9 +1911,9 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
     VirtIONet *n = qemu_get_nic_opaque(nc);
     VirtIONetQueue *q;
     VirtIODevice *vdev = VIRTIO_DEVICE(n);
-    VirtQueueElement *elems[VIRTQUEUE_MAX_SIZE];
-    size_t lens[VIRTQUEUE_MAX_SIZE];
-    struct iovec mhdr_sg[VIRTQUEUE_MAX_SIZE];
+    QEMU_UNINITIALIZED VirtQueueElement *elems[VIRTQUEUE_MAX_SIZE];
+    QEMU_UNINITIALIZED size_t lens[VIRTQUEUE_MAX_SIZE];
+    QEMU_UNINITIALIZED struct iovec mhdr_sg[VIRTQUEUE_MAX_SIZE];
     struct virtio_net_hdr_v1_hash extra_hdr;
     unsigned mhdr_cnt = 0;
     size_t offset, i, guest_offset, j;