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From "Mike Dusenberry (JIRA)" <j...@apache.org>
Subject [jira] [Closed] (SYSTEMML-1563) Add a distributed synchronous SGD MNIST LeNet example
Date Tue, 23 May 2017 00:03:04 GMT

     [ https://issues.apache.org/jira/browse/SYSTEMML-1563?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Mike Dusenberry closed SYSTEMML-1563.
-------------------------------------

> Add a distributed synchronous SGD MNIST LeNet example
> -----------------------------------------------------
>
>                 Key: SYSTEMML-1563
>                 URL: https://issues.apache.org/jira/browse/SYSTEMML-1563
>             Project: SystemML
>          Issue Type: Sub-task
>            Reporter: Mike Dusenberry
>            Assignee: Mike Dusenberry
>             Fix For: SystemML 1.0
>
>
> This aims to add a *distributed synchronous SGD* MNIST LeNet example.  In distributed
synchronous SGD, multiple mini-batches are run forward & backward simultaneously, and
the gradients are aggregated together by addition before the model parameters are updated.
 This is mathematically equivalent to simply using a large mini-batch size, i.e. {{new_mini_batch_size
= mini_batch_size * number_of_parallel_mini_batches}}.  The benefit is that distributed synchronous
SGD can make use of multiple devices, i.e. multiple GPUs or multiple CPU machines, and thus
can speed up training time.  More specifically, using an effectively larger mini-batch size
can yield a more stable gradient in expectation, and a larger number of epochs can be run
in the same amount of time, both of which lead to faster convergence.  Alternatives include
various forms of distributed _asynchronous_ SGD, such as Downpour, Hogwild, etc.  However,
a recent paper \[1] from Google Brain / Open AI has found evidence supporting the claim that
distributed synchronous SGD can lead to faster convergence, particularly if it is extending
with the notion of "backup workers" as described in the paper.
> We will first aim for distributed synchronous SGD with no backup workers, and then extend
this to include backup workers.  The MNIST LeNet model will simply serve as an example, and
this same approach can be extended to more recent models, such as ResNets.
> \[1]: https://arxiv.org/abs/1604.00981



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