On Mon, Feb 25, 2013 at 10:17:08AM +0100, Peter Lieven wrote:
> 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
>
> v3:
> - probe if IFF_ONE_QUEUE feature is available
>
> v2:
> - do only set the flag on linux as it breaks macvtap
> - define IFF_ONE_QUEUE in tap-linux.h
>
> Signed-off-by: Peter Lieven <p...@kamp.de>
Acked-by: Michael S. Tsirkin <m...@redhat.com>
> ---
> net/tap-linux.c | 10 ++++++----
> net/tap-linux.h | 9 +++++----
> 2 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/net/tap-linux.c b/net/tap-linux.c
> index a953189..36c09e2 100644
> --- a/net/tap-linux.c
> +++ b/net/tap-linux.c
> @@ -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 "
> diff --git a/net/tap-linux.h b/net/tap-linux.h
> index 65087e1..5704efb 100644
> --- a/net/tap-linux.h
> +++ b/net/tap-linux.h
> @@ -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
>
> --
> 1.7.9.5
