Kyle McDonald writes: > James Carlson wrote: > > Because it's evil and wrong. ;-} > > > > > Um. Ok. But that doesn't really help me learn *why* it's not technically > possible (or right) to do it, does it? > Fortunately Neil's reply did fill in more of those details.
Sorry about that. That's why I referenced the CR number, forgetting that (a) you're not now a Sun employee, (b) the information was misplaced in the Comments section rather than the evaluation (sigh!) and (c) the broken bug system doesn't allow everyone access to all of the fields needed to read a bug report. > In what way would people shoot themselves in the foot with it? I guess > I'm not seeing the danger? > Is it just the packet ordering overhead Neil mentions? Exactly. If you happen to be running non-IP protocols or if you're doing bridging, then his remarks about standards violations are on target. A bridge, in particular, must not reorder packets and several non-IP protocols can't tolerate reordering in the link layer. However, Solaris doesn't (yet) have bridging integrated, and non-IP support on Solaris is thin, and in the cases where one of those things existed, you could just document that round-robin is inapplicable, so that's not the real reason to avoid doing it. The real reason is that you tend to lose with reordering. There may be a few cases where you win, where the stars all align properly so that reordering is minimal and you end up with N times the throughput. However, there'd also be many cases where the combination would run more slowly than a single link, and you'd end up with escalations and pain. Mike Gerdts writes: > On Fri, May 30, 2008 at 4:15 PM, James Carlson <[EMAIL PROTECTED]> wrote: > > It could certainly be done quite easily, and it's been discussed many > > times. See, for instance, CR 6538146. > > > > I don't really agree with the evaluation of that bug, because > > Can you copy/move the evaluation into a publicly viewable field or > post it as a reply? Here's an excerpt. I've excised the portion that debated the wisdom of including this feature in Sun Trunking. It looks to me less like technical information and more like an email message I shouldn't forward without the author's permission. (The two debating are Martin Lorenz and Nicolas Droux; feel free to contact them to post the material.) This would be clearly against the IEEE802.3ad standard which defines link aggregation. So we cannot support an option which goes against the standards, since we cannot predict the behavior of other systems that would be faced with that traffic. Aside from standard compliance, there are other architectural issues to consider with Solaris: One is of course the performance impact caused by reordering of packets. Also our current stack is heavily relying on the mapping between interrupted cpus and the CPU assigned to the squeue associated with connections. A round robin policy goes completely against that architecture, packets for single connections will start arriving on multiple CPUs, and introducing contention on the squeues associated with these connections, and will lead to performance problems, in addition to the problems caused by reordering. It would also set a precedent, showing that we implement features that go against the architectural principles behind our network stack implementation. -- James Carlson, Solaris Networking <[EMAIL PROTECTED]> Sun Microsystems / 35 Network Drive 71.232W Vox +1 781 442 2084 MS UBUR02-212 / Burlington MA 01803-2757 42.496N Fax +1 781 442 1677 _______________________________________________ networking-discuss mailing list [email protected]
