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https://issues.apache.org/jira/browse/SYSTEMML-1561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15996123#comment-15996123
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Matthias Boehm commented on SYSTEMML-1561:
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sounds great - a second chance would be useful for many other scenarios too.
The 2x runtime improvement is a bit surprising though because very similar
rewrites would be performed during dynamic recompilation (except constant
folding, which is covered by size expression over sub dags of scalar operations
with symbol table inputs) and dynamic recompilation itself was not the
bottleneck. I would be very interested to know were this is coming from, maybe
some cascade of other rewrites/fused operator? You can set
{{ProgramRewriter.LDEBUG = true}} to see the applied simplification rewrites
along with line numbers where they originate from.
For your PR, if you want to ensure that future compiler modifications preserve
this behavior, please add a test into {{functions.recompile}} or
{{functions.misc}}, similar to other size-dependent rewrites - the easiest way
is to construct a case, where without size propagation we would compile/execute
distributed operations and simply compare the number of compiled/executed Spark
instructions with expected values.
> Improve constant folding during compilation
> -------------------------------------------
>
> Key: SYSTEMML-1561
> URL: https://issues.apache.org/jira/browse/SYSTEMML-1561
> Project: SystemML
> Issue Type: Improvement
> Reporter: Mike Dusenberry
> Fix For: SystemML 1.0
>
> Attachments: scenario1_plan.txt, scenario1.py, scenario2_plan.txt,
> scenario2.py
>
>
> In our `nn` library, our convolution and pooling layers have to pass around
> the spatial dimensions (height and width) of the images that are stretched
> out into rows of the input/output matrices. These output dimensions are
> computed within the forward functions of the above layers as small scalar
> equations. From a mathematical standpoint, these sizes can be determined at
> compile time, and it is nice to have these size equations in DML (v.s. hiding
> them inside the engine within built-in functions). However, we do not
> currently evaluate these expressions during compilation, and thus we are left
> with unknown sizes even during recompilation. This naturally leads to max
> memory estimates and thus often leads to unnecessary distributed runtime ops
> rather than simple CP ones.
> I have two related scenarios for which this is a problem. They both involve
> the {{Houtc1}} & {{Woutc1}} values that are returned from a
> `conv2d::forward(...)` function. These represent the spatial dimensions of
> the volume with each of the rows of the output {{outc1}} of the function, and
> the third dimension is {{F1}}. Thus, {{outc1}} has a number of columns equal
> to {{F1*Houtc1*Wouc1}}.
> In the first scenario ({{scenario1.py}}), a random matrix {{doutc1}} is
> created that should have the same dimensions as {{outc1}}. For the columns,
> if I use {{cols=ncol(outc1)}} in this rand statement, the size will be
> propagated and CP ops will be compiled and run. I I instead use
> {{cols=F1*Houtc1*Woutc1}}, the size will forever be unknown, even during
> recompilation, and thus Spark ops will be compiled and run. I have included
> the recompile hops plan ({{scenario1_plan.txt}}).
> In the second scenario ({{scenario2.py}}), a {{max_pool2d::forward(...)}}
> function is inserted after the {{conv2d::forward(...)}} function that
> requires the {{Houtc1}} and {{Woutc1}} variables to be supplied as arguments.
> Since those latter variables are not executed during compilation time, the
> max pooling sizes remain unknown, even during recompilation, and thus Spark
> ops will be compiled and run. I have included the recompile hops plan
> ({{scenario2_plan.txt}}).
> We should either improve or fix our constant folding rewrites so that these
> scenarios are fixed, as they are necessary for performant deep learning
> applications. Note too that this issue will be present in other non-deep
> learning scenarios as well.
> Mailing list thread:
> https://www.mail-archive.com/dev@systemml.incubator.apache.org/msg01657.html
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