On Mon, 2013-06-10 at 10:07 +0300, Michael S. Tsirkin wrote:
> On Thu, Feb 07, 2013 at 01:14:20PM -0500, David Miller wrote:
> > From: Ben Hutchings <bhutchings@xxxxxxxxxxxxxx>
> > Date: Thu, 7 Feb 2013 16:20:46 +0000
> >
> > > If the consensus is still that we must preserve packets exactly (aside
> > > from the usual modifications by IP routers) then LRO should be disabled
> > > on all devices for which forwarding is enabled.
> >
> > I believe this is still undoubtedly the consensus.
>
> With virtio we are getting packets from a linux host,
> so we could thinkably preserve packets exactly
> even with LRO. I am guessing other hardware could be
> doing this as well.
>
> I am not sure what information would need to be preserved -
> could someone help clarify please?
Some LRO implementations may not preserve:
- Packet boundaries
- TSO/GSO produces packets all the same size, except possibly for the
last one. GRO therefore flushes a flow after merging a packet with
a different segment size.
- IPv4 TTL, IPv6 hop-limit, TCP timestamp
- TSO/GSO will put the same values in all packets. GRO flushes a flow
if they change.
- IPv4 fragment ID
- TSO/GSO produces consecutive fragment IDs. GRO flushes a flow
if it sees a non-consecutive fragment ID.
- MAC header, IPv4 TOS, IPv6 traffic class
- Should be the same for all packets in a flow. GRO actually checks
and flushes a flow if they change.
Ben.
--
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
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