tree 1d605e3c657b1eee2cba4bb66e1fbffe23eb88b0
parent a6f4d2ec42f3feb6c399f5760a2567ca78897bd7
author Ilya Maximets <i.maximets@ovn.org> 1695822633 +0200
committer Michael S. Tsirkin <mst@redhat.com> 1696457706 -0400

virtio: use shadow_avail_idx while checking number of heads

We do not need the most up to date number of heads, we only want to
know if there is at least one.

Use shadow variable as long as it is not equal to the last available
index checked.  This avoids expensive qatomic dereference of the
RCU-protected memory region cache as well as the memory access itself.

The change improves performance of the af-xdp network backend by 2-3%.

Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Message-Id: <20230927135157.2316982-1-i.maximets@ovn.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>