Re: [Qemu-devel] [PATCHv2] tap: set IFF_ONE_QUEUE per default

[Christian Borntraeger]

On 15/02/13 15:27, Peter Lieven wrote:
> 
> Am 15.02.2013 um 14:32 schrieb Stefan Hajnoczi <address@hidden>:
> 
>> On Fri, Feb 15, 2013 at 10:32:31AM +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
>>>
>>> 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 <address@hidden>
>>> ---
>>> net/tap-linux.c |    4 ++++
>>> net/tap-linux.h |    1 +
>>> 2 files changed, 5 insertions(+)
>>>
>>> diff --git a/net/tap-linux.c b/net/tap-linux.c
>>> index a953189..d49f2fd 100644
>>> --- a/net/tap-linux.c
>>> +++ b/net/tap-linux.c
>>> @@ -51,6 +51,10 @@ int tap_open(char *ifname, int ifname_size, int 
>>> *vnet_hdr,
>>>     memset(&ifr, 0, sizeof(ifr));
>>>     ifr.ifr_flags = IFF_TAP | IFF_NO_PI;
>>>
>>> +#ifdef __linux__
>>> +    ifr.ifr_flags |= IFF_ONE_QUEUE;
>>> +#endif
>>
>> tap-linux.c  <--- notice the filename
> 
> i know. is qemu really using it on MACs?
> 

It has nothing todo with Apple products. Its about a linux kernel driver that 
provides
a tap like interface that can be attached to an network interface with 
MAC-address 
filtering.

http://virt.kernelnewbies.org/MacVTap

Christian