GitLab

Add features and desires to the PER_VNODE_TT restrictions. For
desires, we can tell the user which ones can't be satisfied, but for
features, we don't even try to figure out which one(s) keep us from
mapping. From the assign_todo file, this is:
9.   add features/desires to PER_VNODE_TT restrictions

Add a new -P switch, when PER_VNODE_TT is in use. This casues it to
prune out pclasses that no vnode can map to - this can lead to _huge_
time savings, particularly since we put things like wide-area nodes
into the ptop file. I've seen a 98% reduction in time when using both
-p and -P! But, it's not the default yet, because I need to do more
testing to make sure that this isn't hurting solution quality
significantly.  todo item:
8.   prune pclasses when using PER_VNODE_TT

Standardize the exit values from assign:
On success, returns 0
On failures that are not retryable (ie. this top can never be mapped
    to this ptop), returns 2
If SA fails to find a solution (ie., we might consider retrying),
    returns 1

Fix a bug that has annoyed me for a very, very long time - if the
input files don't exist, exit instead of hanging forever!

Make the weight at which a feature/desire is considered 'hard' (ie. it
generates a violation if unsatisifed or undesired) a variable, so that
we'll be able to change it from 1.0 if we want.

Put some more messages that should appear inline in the mail to stderr
instead of stdout.

on in production!

PER_VNODE_TT handles emulated links by simply adding up the total bandwidth
consumed by a vnode, and the total bandwidth available on each pnode. Of
course, this can lead to false positives (knapsack problem), but that's okay,
because it just means we won't bail up front - we'll have to do the full
annealing pass before we decide it's unmappable.

PER_VNODE_TT now also tries to figure out why a vnode is not mappable - if
there are _no_ pclasses that match one of the restrictions, it will print out
something like:
  *** No possible mapping for nodeA
      Too many links!
  *** No possible mapping for nodeB
      Too much bandwidth on emulated links!

This completes the following two items from assign_todo.txt:

6.   fix PER_VNODE_TT and vclasses
7.   fix PER_VNODE_TT and emulated vlinks

go on the end of a link line in the top file, trivial_ok . This means
that it's okay to map the virtual link to a trivial link. By default,
it will not be permissible to use trivial links.

Right now, however, trivial links are OK by default, but that will
change once assign_wrapper flags all simulated links as trivial_ok .

using the new assign, and captures Leigh's linkdelays work.

time to debug a delayed LAN problem.

In addition to assign, assign_wrapper and ptopgen have been modified
to output the new formats used by assign.

with other emulated links.  Also added a trivial link type for virtual
links between vnodes in the same pnode.

make-vclass A 0.5 pc600 pc850

in the top file.  And then have nodes of type A.  Assign will try to put
them all as either pc600 or pc850.

Still need to write all the pre-assign stuff.

This check-in consists of 7 modifications to assign.

1. Equivalence Classes

Defined an equivalence relation on the physical nodes and applied it
to the physical topology to get the resulting quotient topology (abuse
of terminology).  So instead of searching among all possible physical
nodes to make a map, assign only searches among all possible
equivalence classes of nodes.  This tremendously reduces the search
space.  At the time of this writing it reduces the physical topology
from 252 nodes to 13 nodes.  The equivalence classes are generated
automatically from the ptop file.

2. Scoring based on equivalence classes.

Each equivalence class used comes with a significant cost.  This
strongly encourages assign to use equivalence machines when possible.
The result is that an experiment that does not otherwise specify will
almost definitely get machines of the same type.  If this needs to be
reduced in the future it is the SCORE_PCLASS constant.

3. Heuristics

Added a bunch of heuristics for choosing which equivalence class to
use.  This was less successful than I hoped.  A good solution is now
found in record time but it still continues searching.  When OPTIMAL
is turned on these heuristics help a lot.  When off they make little
difference.  I may turn this into a compile time option in the future
since the heuristics do take non-trivial CPU cycles.

4. Fixed the very-very-big-and-evil disconnected-switches bug.

Assign wasn't cleaning up after itself in certain cases.  Disconnected
graphs are now merely a minor, easily ignored, bump rather than the
towering cliffs they use to be.

5. Fixed the not-yet-noticed not-enough-nodes bug.

Found a bug that probably has never come up before because we have
checks that avoid those circumstances.

6. Modified constants.

I was tired of waiting so long for results so, I lowered CYCLES and
reduced the constant for naccepts (Mac, you probably want to add that
inconspicuous number to your configurable constants; look for
"naccepts =").  The results is roughly a speedup of 2.  It works great
currently but we may want to change these numbers up again if we get
problems with features and desires.

7. General clean up.

Associated with the other changes was a lot of restructuring and some
cleanup.  Specifically to the assign loop and scoring code.

now precomputers the shortest path between all pairs of switches and uses
this to computer paths through the switch fabric.  In the process of
writing this I also removed the limitations of two switch hops.  Packets
can now travel through any number of switches to reach their destination.
Of course, the longer the path the more it costs so assign will prefer
shorter paths.

Also did various other tweaks in the process.  We now use strings almost
everywhere instead of char*'s and the makefile is cleaner.

Added a basic README

Added two tests for features/desires.