Re: gso: Attempt to handle mega-GRO packets

Jason Wang
2013-11-07T02:53:21Z

On 11/07/2013 08:36 AM, Herbert Xu wrote:
> On Wed, Nov 06, 2013 at 07:01:10AM -0800, Eric Dumazet wrote:
>> Have you thought about arches having PAGE_SIZE=65536, and how bad it is
>> to use a full page per network frame ? It is lazy and x86 centered.
> So instead if we were sending a full 64K packet on such an arch to
> another guest, we'd now chop it up into 1.5K chunks and reassemble them.
>
>> So after our patches, we now have an optimal situation, even on these
>> arches.
> Optimal only for physical incoming packets with no jumbo frames.
>
> What's worse, I now realise that the coalesce thing isn't even
> guaranteed to work. It probably works in your benchmarks because
> you're working with freshly allocated pages.
>
> But once the system has been running for a while, I see nothing
> in the virtio_net code that tries to prevent fragmentation. Once
> fragmentation sets in, you'll be back in the terrible situation
> that we were in prior to the coalesce patch.
>
> Jason/Michael (Tsirkin), am I missing something that would prevent
> fragmentation of these buffers?
>
> Cheers,

No. Maybe we can use per-queue buffers instead.