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tap: set IFF_ONE_QUEUE per default 

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>
master
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
Show Stats 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 "

9
net/tap-linux.h
View File

@ -34,10 +34,11 @@
#endif
/* TUNSETIFF ifr flags */
#define IFF_TAP 0x0002
#define IFF_NO_PI 0x1000
#define IFF_VNET_HDR 0x4000
#define IFF_MULTI_QUEUE 0x0100
#define IFF_TAP 0x0002
#define IFF_NO_PI 0x1000
#define IFF_ONE_QUEUE 0x2000
#define IFF_VNET_HDR 0x4000
#define IFF_MULTI_QUEUE 0x0100
#define IFF_ATTACH_QUEUE 0x0200
#define IFF_DETACH_QUEUE 0x0400