[libvirt] [PATCH] Enable tuning of qemu network tap device "sndbuf" size

[Laine Stump]

On 01/13/2011 04:21 PM, Eric Blake wrote:
> On 01/12/2011 11:45 PM, Laine Stump wrote:
>> This is in response to a request in:
>>
>>     https://bugzilla.redhat.com/show_bug.cgi?id=665293
>>
>> In short, under heavy load, it's possible for qemu's networking to
>> lock up due to the tap device's default 1MB sndbuf being
>> inadequate. adding "sndbuf=0" to the qemu commandline -netdevice
>> option will alleviate this problem (sndbuf=0 actually sets it to
>> 0xffffffff).
>>
>> Because we must be able to explicitly specify "0" as a value, the
>> standard practice of "0 means not specified" won't work here. Instead,
>> virDomainNetDef also has a sndbuf_specified, which defaults to 0, but
>> is set to 1 if some value was given.
>>
>> The sndbuf value is put inside a<tune>  element of each<interface>  in
>> the domain. The intent is that further tunable settings will also be
>> placed inside this elemnent.
> s/elemnent/element/

Fixed.

>> Also, as with the vhost patch, I didn't get the html docs updated for
>> this addition either. I will add both in a single followup patch next
>> week.
> Added to my list of things to remind you about, if you forget :)

Also on my own list.


> Oh, we don't have virStrToLong_ul.

Now can be changed to "we *didn't* have virStrToLong_ul" :-) Thanks!

I changed all the sndbuf things to unsigned long, and have also changed 
sndbuf_specified to a bool in v2.