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tap: set IFF_ONE_QUEUE per default

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historically the kernel queues packets two times. once
at the device and second in qdisc. this is believed to cause
interface stalls if one of these queues overruns.

setting IFF_ONE_QUEUE is the default in kernels >= 3.8. the
flag is ignored since then. see kernel commit
5d097109257c03a71845729f8db6b5770c4bbedc

Signed-off-by: Peter Lieven <pl@kamp.de>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Peter Lieven 2013-02-25 10:17:08 +01:00 • committed by Stefan Hajnoczi
parent ce675a7579
commit d26e445c80
2 changed files with 11 additions and 8 deletions
Download patch file Download diff file Expand all files Collapse all files

10
net/tap-linux.c
View file

@ -42,6 +42,7 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
struct ifreq ifr;
int fd, ret;
int len = sizeof(struct virtio_net_hdr);
unsigned int features;
TFR(fd = open(PATH_NET_TUN, O_RDWR));
if (fd < 0) {
@ -51,9 +52,12 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
memset(&ifr, 0, sizeof(ifr));
ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
if (*vnet_hdr) {
unsigned int features;
if (ioctl(fd, TUNGETFEATURES, &features) == 0 &&
features & IFF_ONE_QUEUE) {
ifr.ifr_flags |= IFF_ONE_QUEUE;
}
if (*vnet_hdr) {
if (ioctl(fd, TUNGETFEATURES, &features) == 0 &&
features & IFF_VNET_HDR) {
*vnet_hdr = 1;
@ -78,8 +82,6 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
}
if (mq_required) {
unsigned int features;
if ((ioctl(fd, TUNGETFEATURES, &features) != 0) ||
!(features & IFF_MULTI_QUEUE)) {
error_report("multiqueue required, but no kernel "