does it also happen when you actually enable RSS in the kernel? Since like I went through a whole lot of pain to assign a flowid at connection setup time.
-a On 4 January 2018 at 15:37, Steven Hartland <ste...@multiplay.co.uk> wrote: > > > On 04/01/2018 22:42, hiren panchasara wrote: > > On 01/04/18 at 09:52P, Steven Hartland wrote: > > On 04/01/2018 20:50, Eugene Grosbein wrote: > > 05.01.2018 3:05, Steven Hartland wrote: > > Author: smh > Date: Thu Jan 4 20:05:47 2018 > New Revision: 327559 > URL: https://svnweb.freebsd.org/changeset/base/327559 > > Log: > Disabled the use of flowid for lagg by default > > Disabled the use of RSS hash from the network card aka flowid for > lagg(4) interfaces by default as it's currently incompatible with > the lacp and loadbalance protocols. > > The incompatibility is due to the fact that the flowid isn't know > for the first packet of a new outbound stream which can result in > the hash calculation method changing and hence a stream being > incorrectly split across multiple interfaces during normal > operation. > > This can be re-enabled by setting the following in loader.conf: > net.link.lagg.default_use_flowid="1" > > Discussed with: kmacy > Sponsored by: Multiplay > > RSS by definition has meaning to received stream. What is "outbound" stream > in this context, why can the hash calculatiom method change and what exactly > does it mean "a stream being incorrectly split"? > > Yes RSS is indeed a received stream but that is used by lagg for lacp > and loadbalance protocols to decide which port of the lagg to "send" the > packet out of. As the flowid is not known when a new "output" stream is > instigated the current code falls back to manual hash calculation to > determine which port to send the initial packet from. Once a response is > received a tx then uses the flowid. This change of hash calculation > method can result in the initial packet being sent from a different port > than the rest of the stream; this is what I meant by "incorrectly split". > > For my understanding, is this just an issue for the first packet when we > originate the flow? Once we have a response and if flowid is there, we'd > use it, right? OR am I missing something? > > Initially yes, but that can cause a whole cascading set of problems. If the > source machine sends from two different ports then flow can traverse across > the network using different paths and hence arrive at the destination on > different ports too, causing the corresponding issue on the other side. > > And with this change, we'd always go and do manual calculation even when > we have a valid flowid (i.e. we didn't initiate a connection)? > > Correct, but there's potentially no easy way to correctly determine what the > flowid and hence hash should be in this case, likely impossible if the lagg > consists of different interface types. > > In addition if the hardware hash doesn't match the requested one as per > laggproto then additional issues could also be triggered. > > Our TCP stack seems fragile during setup to out of order packets which this > multipath behavior causes, we've seen this on our loadbalancers which is > what triggered the investigation. The concrete result is many aborted TCP > connections, over 300k ~2% on the machine I'm looking at. > > I hope there's some improvements that can be made, for example if we can > determine the stream was instigated remotely then flowid would always be > valid hence we can use it assuming it matches the requested spec or if we > can make it clear to the user that laggproto is not the one they requested, > I'm open to ideas? > > Regards > Steve > _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
