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Merge pull request #2405 from minrk/paralleldoc...
Min RK -
r8447:48dd8a34 merge
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@@ -386,19 +386,20 b' weighted: Weighted Two-Bin Random'
386 386 Greedy Assignment
387 387 -----------------
388 388
389 Tasks are assigned greedily as they are submitted. If their dependencies are
389 Tasks can be assigned greedily as they are submitted. If their dependencies are
390 390 met, they will be assigned to an engine right away, and multiple tasks can be
391 391 assigned to an engine at a given time. This limit is set with the
392 ``TaskScheduler.hwm`` (high water mark) configurable:
392 ``TaskScheduler.hwm`` (high water mark) configurable in your
393 :file:`ipcontroller_config.py` config file, with:
393 394
394 395 .. sourcecode:: python
395 396
396 397 # the most common choices are:
397 c.TaskSheduler.hwm = 0 # (minimal latency, default in IPython ≤ 0.12)
398 c.TaskSheduler.hwm = 0 # (minimal latency, default in IPython < 0.13)
398 399 # or
399 c.TaskScheduler.hwm = 1 # (most-informed balancing, default in > 0.12)
400 c.TaskScheduler.hwm = 1 # (most-informed balancing, default in ≥ 0.13)
400 401
401 In IPython ≤ 0.12,the default is 0, or no-limit. That is, there is no limit to the number of
402 In IPython < 0.13, the default is 0, or no-limit. That is, there is no limit to the number of
402 403 tasks that can be outstanding on a given engine. This greatly benefits the
403 404 latency of execution, because network traffic can be hidden behind computation.
404 405 However, this means that workload is assigned without knowledge of how long
@@ -406,10 +407,10 b' each task might take, and can result in poor load-balancing, particularly for'
406 407 submitting a collection of heterogeneous tasks all at once. You can limit this
407 408 effect by setting hwm to a positive integer, 1 being maximum load-balancing (a
408 409 task will never be waiting if there is an idle engine), and any larger number
409 being a compromise between load-balance and latency-hiding.
410 being a compromise between load-balancing and latency-hiding.
410 411
411 412 In practice, some users have been confused by having this optimization on by
412 default, and the default value has been changed to 1. This can be slower,
413 default, so the default value has been changed to 1 in IPython 0.13. This can be slower,
413 414 but has more obvious behavior and won't result in assigning too many tasks to
414 415 some engines in heterogeneous cases.
415 416
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