Date: Fri, 5 Jan 2018 09:44:25 +0000 From: Steven Hartland <steven@multiplay.co.uk> To: Adrian Chadd <adrian.chadd@gmail.com> Cc: hiren panchasara <hiren@strugglingcoder.info>, Eugene Grosbein <eugen@grosbein.net>, src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r327559 - in head: . sys/net Message-ID: <4b7b011a-9fe3-f0ec-04a0-c201a2cfcfda@multiplay.co.uk> In-Reply-To: <CAJ-Vmom8jOsMnzVX276JRe5kN-OM%2BCH%2B6LKtEL_hCgh6-XD2kg@mail.gmail.com> References: <201801042005.w04K5liB049411@repo.freebsd.org> <5A4E9397.9000308@grosbein.net> <f133b587-1f7e-4594-31d1-974775ad55be@freebsd.org> <20180104224214.GD18879@strugglingcoder.info> <63c3c450-aeaf-bdd5-5e16-414146c9bb3a@multiplay.co.uk> <CAJ-Vmom8jOsMnzVX276JRe5kN-OM%2BCH%2B6LKtEL_hCgh6-XD2kg@mail.gmail.com>
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I found https://wiki.freebsd.org/NetworkRSS but I couldn't see any options mentioned, is there a sysctl or kernel option for that Adrian? For reference our current test is on a production LB running 11.0-RELEASE. We're in the process of updating our HEAD box for additional testing. On 05/01/2018 02:55, Adrian Chadd wrote: > 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 <steven@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 >>
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