[ofa-general] [OPENSM PATCH 0/5]: New "guid-routing-order" option for updn routing

[Al Chu]

Hey Sasha,

This is a conceptually simple option I've developed for updn routing.

Currently in updn routing, nodes/guids are routed on switches in a
seemingly-random order, which I believe is due to internal data
structure organization (i.e. cl_qmap_apply_func is called on
port_guid_tbl) as well as how the fabric is scanned (it is logically
scanned from a port perspective, but it may not be logical from a node
perspective).  I had a hypothesis that this was leading to increased
contention in the network for MPI.

For example, suppose we have 12 uplinks from a leaf switch to a spine
switch.  If we want to send data from this leaf switch to node[13-24],
the up links we will send on are pretty random. It's because:

A) node[13-24] are individually routed at seemingly-random points based
on when they are called by cl_qmap_apply_func().

B) the ports chosen for routing are based on least used port usage.

C) least used port usage is based on whatever was routed earlier on.

So I developed this patch series, which supports an option called
"guid_routing_order_file" which allows the user to input a file with a
list of port_guids which will indicate the order in which guids are
routed instead (naturally, those guids not listed are routed last).  I
list the port guids of the nodes of the cluster from node0 to nodeN, one
per line in the file.  By listing the nodes in this order, I believe we
could get less contention in the network.  In the example above, sending
to node[13-24] should use all of the 12 uplinks, b/c the ports will be
equally used b/c nodes[1-12] were routed beforehand in order.

The results from some tests are pretty impressive when I do this. LMC=0
average bandwidth in mpiGraph goes from 391.374 MB/s to 573.678 MB/s
when I use guid_routing_order.  A variety of other positive performance
increases were found when doing other tests, other MPIs, and other LMCs
if anyone is interested.

BTW, I developed this patch series before your preserve-base-lid patch
series.  It will 100% conflict with the preserve-base-lid patch series.
I will fix this patch series once the preserve-base-lids patch series is
committed to git.  I'm just looking for comments right now.

Al

-- 
Albert Chu
chu11 at llnl.gov
925-422-5311
Computer Scientist
High Performance Systems Division
Lawrence Livermore National Laboratory