mpi: Prevent parallel halo exchanges#2972
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| # the first nest triggering all necessary halo exchanges along `f` | ||
| mapper = as_mapper(found, lambda c1: c1.ispace) | ||
| for k, v in mapper.items(): | ||
| mapper = as_mapper(found, lambda c1: (c1.ispace, c1.properties)) |
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How does c1.properties end up being used here?
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that's the actual bug fix
if you don't use the HaloTouch's properties, where the d loop in correctly tagged as sequential, but rather reuse c's properties via rebuild (main's behaviour) then d may erroneously be tagged as parallell depending on its status in c
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Oh, so the rebuild was actually changing the properties of the innermost dimension of the cluster?
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not quite. We were using the rebuild to create a new Cluster -- a Cluster whose sole purpose was carrying a halo_scheme. But using c's rebuild cause us inheriting the wrong properties
| for v in mapper.values(): | ||
| hs = HaloScheme.union([c1.halo_scheme for c1 in v]) | ||
| processed.append(c.rebuild(exprs=[], ispace=k, halo_scheme=hs)) | ||
| processed.append(v[0].rebuild(exprs=[], halo_scheme=hs)) |
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Isn't this changing the type being appended to processed from Cluster to IterationSpace?
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no, v[0] is any c1 within v, that is, a Cluster
if what you said were true, many many tests would fail badly
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Ah ok, this is from me misunderstanding as_mapper
| halo_update = tloop.nodes[0].body[0].body[0].body[0] | ||
| assert isinstance(halo_update, HaloUpdateList) | ||
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| @pytest.mark.parallel(mode=4) |
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The incorrect code still gets generated with 1 rank of MPI fwiw. It also won't hang CI in this configuration if it does go wrong, and will instead fail on the structure tests
| g = Function(name="g", grid=grid, space_order=8, dimensions=(x, y, d), shape=(n, n, 2)) | ||
| h = g.func(name='h') | ||
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| eqns = [Eq(a, 0.0), |
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Some of these equations can be dropped or simplified iirc. I had something along the lines of:
eqns = [Eq(h, 1), Inc(a, h.dx + h.dy)]which also allows for the Functions to be tidied up
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yes, I know, but I don't think it hurts to leave it a little bit more convoluted, in this particular case and based on what I see while I was debugging it
| assert iters[2].dim is d and iters[2].is_Parallel | ||
| assert iters[3].dim is d and iters[3].is_Sequential | ||
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| # Probably unnecessary, but ensures there's no hanging |
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Hanging CI is annoying at best and I agree the .apply() is overkill
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it won't hang anyway since we run it under a timeout of 300 secs -- not sign of life in 5 mins => death
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Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #2972 +/- ##
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- Coverage 83.55% 83.53% -0.03%
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Files 257 257
Lines 53558 53576 +18
Branches 4585 4585
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+ Hits 44751 44755 +4
- Misses 8013 8028 +15
+ Partials 794 793 -1
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