Date: Tue, 29 Oct 2013 15:35:40 -0400 From: Randall Stewart <rrs@lakerest.net> To: Andre Oppermann <andre@FreeBSD.org> Cc: net@FreeBSD.org Subject: Re: MQ Patch. Message-ID: <A3A878D4-A157-430D-A023-EB1607DE9E5B@lakerest.net> In-Reply-To: <526FFED9.1070704@freebsd.org> References: <40948D79-E890-4360-A3F2-BEC34A389C7E@lakerest.net> <526FFED9.1070704@freebsd.org>
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On Oct 29, 2013, at 2:30 PM, Andre Oppermann wrote: > On 29.10.2013 11:50, Randall Stewart wrote: >> Hi: >>=20 >> As discussed at vBSDcon with andre/emaste and gnn, I am sending >> this patch out to all of you ;-) >=20 > I wasn't at vBSDcon but it's good that you're sending it (again). ;) >=20 >> I have previously sent it to gnn, andre, jhb, rwatson, and several = other >> of the usual suspects (as gnn put it) and received dead silence. >=20 > Sorry 'bout that. Too many things going on recently. >=20 >> What does this patch do? >>=20 >> Well it add the ability to do multi-queue at the driver level. = Basically >> any driver that uses the new interface gets under it N queues = (default >> is 8) for each physical transmit ring it has. The driver picks up >> its queue 0 first, then queue 1 .. up to the max. >=20 > To make I understand this correctly there are 8 soft-queues for each = real > transmit ring, correct? And the driver will dequeue the lowest = numbered > queue for as long as there are packets in it. Like a hierarchical = strict > queuing discipline. >=20 > This is prone to head of line blocking and starvation by higher = priority > queues. May become a big problem under adverse traffic patterns. Thats the whole idea of QOS.. you take and prioritize your traffic if you don't have enough b/w. The guys at the bottom get none..=20 If you don't want it, you can either turn QOS off.. i.e. let everything fall to the bottom bucket. Or even set the number of queues to 1, and then nothing changes 1:1 queues to transmit-ring >=20 >> This allows you to prioritize packets. Also in here is the start of = some >> work I will be doing for AQM.. think either Pi or Codel ;-) >>=20 >> Right now thats pretty simple and just (in a few drivers) as the = ability >> to limit the amount of data on the ring=85 which can help reduce = buffer >> bloat. That needs to be refined into a lot more. >=20 > We actually have two queues, the soft-queue and the hardware ring = which > both can be rather large leading to various issues as you mention. Which is why I first of all set the soft-queue default at 64.. That in some ways is still big. In order to get rid of the hard-queue you really just have to limit how much you put in. I have some hooks in for igb here (and em) that do this but its just a first step. The right thing (long term) is to go to a AQM like Codel or Pi.=20 Pi would give you coverage of both queue's at ingress to the first one = (thinking of a single queue model) Codel can only handle the soft-> hard queue transition. But Pi has the standard Cisco patent so it will probably have to be a loadable module=85 sigh.. >=20 > I've started work on an FF contract to rethink the whole IFQ* model = and What is an FF contract? > to propose and benchmark different approaches. After that to convert = all > drivers in the tree to the chosen model(s) and get rid of the legacy. = In > general the choice of model will be done in the driver and no longer = by > the ifnet layer. One or (most likely) more optimized models will be > provided by the kernel for drivers to chose from. The idea that most, > if not all drivers use these standard kernel provided models to avoid > code duplication. However as the pace of new features is quite high > we provide the full discretion for the driver to choose and experiment > with their own ways of dealing with it. This is under the assumption > that once a now model has been found it is later moved to the kernel > side and subsequently used by other drivers as well. >=20 >> This work is donated by Adara Networks and has been discussed in = several >> of the past vendor summits. >>=20 >> I plan on committing this before the IETF unless I hear major = objections. >=20 > There seems to be a couple of white space issues where first there is = a tab > and then actual whitespace for the second one and others all over the = place. >=20 > There seem to be a number of unrelated changes in sys/dev/cesa/cesa.c, > sys/dev/fdt/fdt_common.c, sys/dev/fdt/simplebus.c, = sys/kern/subr_bus.c, > usr.sbin/ofwdump/ofwdump.c. >=20 Yeah Fabien Thomas and I have already talked on that. I had some hold over cruft that I had thought I got out. The cesa.c changes I committed this AM and the debug stuff was all reverted out. Plus a couple of other little tweaks. I will resend an updated (cleaned up patch) once my build-universe = completes :-) > It would be good to separate out the soft multi-queue changes from the = ring > depth changes and do each in at least one commit. I am not sure what you are suggesting here.=20 >=20 > There are two separate changes to sys/dev/oce/, one is renaming of the = lock > macros and the other the change to drbr. Yeah I hit that because the LOCK name unfortunately conflicted with = another so on one of my build-universe runs LINT would blow up ;-( That could definitely be done separately.. >=20 > The changes to sys/kern/subr_bufring.c are not style compliant and we = normally > don't use Linux "wb()" barriers in FreeBSD native code. The atomics_* = should > be used instead. >=20 Those are taken *directly* the original code put in by Kip.. I just = moved them over when I was refactoring things. > Why would we need a multi-consumer dequeue? I can think of one reason.. its called lagg=20 R >=20 > The new bufring functions on a first glance do seem to be safe on = architectures > with a more relaxed memory ordering / cache coherency model than x86. >=20 > The atomic dance in a number of drbr_* functions doesn't seem to make = much sense > and a single spin-lock may result in atomic operations and bus lock = cycles. >=20 > There is a huge amount of includes pollution in sys/net/drbr.h which = we are > currently trying to get rid of and to avoid for the future. >=20 >=20 > I like the general conceptual approach but the implementation feels = bumpy and > not (yet) ready for prime time. In any case I'd like to take forward = conceptual > parts for the FF sponsored IFQ* rework. >=20 > --=20 > Andre >=20 > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org" >=20 ------------------------------ Randall Stewart 803-317-4952 (cell)
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