On 15/02/13 10:25, Peter Lieven wrote: > > Am 15.02.2013 um 10:22 schrieb Christian Borntraeger <borntrae...@de.ibm.com>: > >> On 15/02/13 09:27, 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 >>> >>> Signed-off-by: Peter Lieven <p...@kamp.de> >>> --- >>> net/tap-linux.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/net/tap-linux.c b/net/tap-linux.c >>> index a953189..2759b78 100644 >>> --- a/net/tap-linux.c >>> +++ b/net/tap-linux.c >>> @@ -49,7 +49,7 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, >>> return -1; >>> } >>> memset(&ifr, 0, sizeof(ifr)); >>> - ifr.ifr_flags = IFF_TAP | IFF_NO_PI; >>> + ifr.ifr_flags = IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE; >>> >>> if (*vnet_hdr) { >>> unsigned int features; >> >> Wouldn't that break macvtap? >> >> there is >> >> case TUNSETIFF: >> /* ignore the name, just look at flags */ >> if (get_user(u, &ifr->ifr_flags)) >> return -EFAULT; >> >> ret = 0; >> if ((u & ~IFF_VNET_HDR) != (IFF_NO_PI | IFF_TAP)) >> ret = -EINVAL; >> >> >> in drivers/net/macvtap.c >> >> > > wasn`t aware I will modify this to only be set on linux > > Peter
macvtap is a Linux driver. It is given to qemu usually via libvirt with something like -netdev tap,fd=21,id=hostnet0,vhost=on,vhostfd=22 and then having fd21 pointing to an open /dev/tap... device which is backed by macvtap. Christian