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

[Peter Lieven]

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?

Peter

> 
> Perhaps the solution is to try with IFF_ONE_QUEUE.  If the result is
> -EINVAL, try without.
> 
> Stefan