From 9f9c5b4e9f0c230e81167f937d9d875a67e4558b Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= Date: Tue, 10 Jun 2025 13:36:59 +0100 Subject: [PATCH 29/43] hw/net/virtio-net: skip automatic zero-init of large arrays MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit RH-Author: Stefan Hajnoczi RH-MergeRequest: 381: Solve -ftrivial-auto-var-init performance regression with QEMU_UNINITIALIZED RH-Jira: RHEL-95479 RH-Acked-by: Miroslav Rezanina RH-Commit: [21/31] 87ec97d9e701b7ee27f4b728f0622f5b730e1c03 (stefanha/centos-stream-qemu-kvm) 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 Reviewed-by: Stefan Hajnoczi Message-id: 20250610123709.835102-22-berrange@redhat.com Signed-off-by: Stefan Hajnoczi (cherry picked from commit 21cf31c51a7aeff4270c9b30b37e019c536d54b2) Signed-off-by: Stefan Hajnoczi --- hw/net/virtio-net.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index bd37651dab..aaa024d70c 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -1910,9 +1910,9 @@ 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; -- 2.39.3