[Beowulf] ethernet bonding performance comparison "802.3ad" vs Adaptive Load Balancing

Rahul Nabar rpnabar at gmail.com
Wed Sep 17 17:18:39 EDT 2008


On Wed, Sep 17, 2008 at 4:05 PM, Eric Thibodeau <kyron at neuralbs.com> wrote:

>Well, apart from the fact that ssh is compressed and, as Digo pointed out and that 47 MB/sec is probably your HDD's transfer capacity as >Shannon pointed out, also keep in mind your bus's capacity ( http://en.wikipedia.org/wiki/List_of_device_bandwidths is a nice list). So, >unless you've got both NICs on PCI-E (or independant PCI channels, which I've only heard of in high-end Compaq servers with hotswap PCI >interfaces)  you're saturating your bus.

Thanks for all those responses guys! Eric; I'll check my bus speed; my
server is not very high end. These are Dell Power Edge 1435's. But
after I first posted I did a couple more debugs and diagnostics:

(1) As Shannon pointed earlier, I did give netperf a shot now. Funny
resut is this:

If I netperf from Machine A to B I get only 1Gbps.
If I start two netperfs on A and try to talk to B ; each gets 0.5Gbps.
Thus aggregate of still 1 Gbps
BUT if I start two netperfs on A and one talks to B and another to C
each gets 1 Gbps. Thus I got an aggregate of 2 Gbps out [desired
result]
In the last situation if I disable one link then I fall back to 0.5
Gbps each. So this is my (almost) perfect situation.

Forces me to conclude that I am _not_ disk, bus nor I/O limited. What
do you think?

The sad thing though is this: I could never get a peer-to-peer (A
talks to B alone) mode that would give me a 2 Gbps aggregated. This is
frustrating. These are 8 cpu/node servers and frequently even a 16 cpu
job will span across only 2 compute-nodes. Then if I cannot use both
the eth cards it seems an awful waste of capacity. Just think about
this: If two-processes talk from A-to-B I get 1 Gbps aggregate. But if
I have two processes and just route one through a
passive-forwarding-machine C (thus A-to-B and A-to-C-to-B) then I will
end up with an aggregate of 2 Gbps. This seems a very strange,
non-intuitive and undesirable outcome of the current bonding setup , I
feel.

I might have to actually _force_ jobs to span more than two servers
just to be able to use both my eth cards! Feels very strange to me.

I tried both modes 4 and 6. Rick Jones, the netperf maintainer gave me
a very promising suggestion that I might be able to modify my bonding
hash algorithm so that it bonds traffic coming from two different
processes originating on the same node. Currently I cannot. Anybody
else has given this a shot?

I'm eager to hear any other comments people might have.

-- 
Rahul
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