[Computer-go] Fuego in Kanazawa and UEC Cup

Richard B Segal rsegal at us.ibm.com
Tue Nov 30 09:13:40 PST 2010


Yes, there are many possible variations / enhancements to virtual loss.   I
have found
experimentally that the +1 variety is sufficient for near perfect scaling
to hundreds of
threads so it is not clear that any additional improvement is needed.

- Rich


computer-go-bounces at dvandva.org wrote on 11/30/2010 12:48:54 AM:

> [image removed]
>
> Re: [Computer-go] Fuego in Kanazawa and UEC Cup
>
> Michael Williams
>
> to:
>
> computer-go
>
> 11/30/2010 12:49 AM
>
> Sent by:
>
> computer-go-bounces at dvandva.org
>
> Please respond to computer-go
>
> Since you brought up virtual losses, I wanted to point-out something
> that occurred to me recently:  you don't have to use just one virtual
> loss.  You can add N visits to a node when you visit it and then
> remove N-1 visits when you update the node with the playout result.
> The larger N is, the less different threads will step on each other.
> Of course increasing N also means an increased likelyhood of exploring
> irrelevant paths.
>
>
>
> On Mon, Nov 29, 2010 at 4:33 PM, Richard B Segal <rsegal at us.ibm.com>
wrote:
> > Hi Everyone,
> >
> > Aja's description of Fuego in the UEC cup is pretty accurate. The main
> > changes to Fuego for both events were to improve scaling on the 112
core
> > system. The move generation algorithm was mostly identical to the SVN
source
> > for both Kanazawa and the first day of the UEC cup.
> >
> > We did make a possibly significant change for the last two matches of
the
> > UEC cup. Once in Kanazawa and once on the first day of the UEC cup
Fuego
> > lost by attacking with a ladder that would ultimately fail. Fuego has a
root
> > filter that prevents extending a group that will be captured in a
ladder,
> > but it does not filter failed attacks. I modified Fuego's root filter
for
> > the last two matches to remove failed attacks as well. I also modified
the
> > code to apply the root filter (minus its safety check) at all levels of
the
> > search. While the new code did not show any improvement in self play,
it did
> > improve its handling of the position that led to the failed
ladderattack in
> > the UEC match against Erica.
> >
> > The other change between Kanazawa and the UEC cup was regarding some
> > experimental code to improve exploration. The experimental code appears
to
> > be effective for 9x9 play, but its value for 19x19 play was
questionable. I
> > had weak experimental data (50 games) in Kanazawa suggesting it may be
> > useful so I enabled it for 19x19 as well. A similar weak experiment
just
> > before the UEC cup showed a 50 ELO loss so it was disabled for the UEC
cup.
> >
> > Probably the most important change for running on the 56 core system
was
> > switching from floats to doubles to score move evaluations. After about
one
> > million trials, the limited precision of floats becomes a bottleneck to
> > improved play. I made a few small modifications to the virtual loss
code to
> > ensure that virtual losses were added as early as possible, and removed
as
> > late as possible to maximize their effect. I also separated out the
counting
> > of virtual losses from the UCT statistics to reduce the chances of
> > simultaneous updates as simultaneous updates can introduce counting
errors.
> >
> > The final addition was a new parallel tree copy algorithm that was
needed
> > due to the large 200Gb RAM available on the 56 core system. When Fuego
runs
> > out of memory, it copies its current tree to a new tree while removing
nodes
> > with a small number of trials. The single threaded copy algorithm took
up to
> > 20 seconds on a 200Gb tree. The parallel tree copy algorithm reduces
the
> > same copy to about 4 seconds.
> >
> > We plan to eventually move most if not all of these updates into the
public
> > Fuego source tree. For completeness, the configuration script used for
UEC
> > was as follows:
> >
> > go_rules japanese
> > time_settings 1800 0 0
> > komi 6.5
> >
> > uct_max_memory 175000000000
> >
> > uct_param_player ponder 1
> > uct_param_player reuse_subtree 1
> >
> > uct_param_search lock_free 1
> > uct_param_search number_threads 112
> > uct_param_search number_playouts 2
> >
> > # Enable new parallel tree copy
> > uct_param_search max_copy_threads 8
> >
> > # New features added on second day of UEC cup
> > uct_param_globalsearch use_filter 1
> > uct_param_rootfilter check_offensive_ladders 1
> >
> > - Rich
> >
> > _______________________________________________
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> > Computer-go at dvandva.org
> > http://dvandva.org/cgi-bin/mailman/listinfo/computer-go
> >
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