From d2d5e360b62b86606ac753ed75c6f1c5ebc49002 2012-01-20 00:00:29 From: MinRK Date: 2012-01-20 00:00:29 Subject: [PATCH] document new default hwm value --- diff --git a/docs/source/parallel/parallel_task.txt b/docs/source/parallel/parallel_task.txt index a869d48..775f0a3 100644 --- a/docs/source/parallel/parallel_task.txt +++ b/docs/source/parallel/parallel_task.txt @@ -415,11 +415,11 @@ assigned to an engine at a given time. This limit is set with the .. sourcecode:: python # the most common choices are: - c.TaskSheduler.hwm = 0 # (minimal latency, default) + c.TaskSheduler.hwm = 0 # (minimal latency, default in IPython ≤ 0.12) # or - c.TaskScheduler.hwm = 1 # (most-informed balancing) + c.TaskScheduler.hwm = 1 # (most-informed balancing, default in > 0.12) -The default is 0, or no-limit. That is, there is no limit to the number of +In IPython ≤ 0.12,the default is 0, or no-limit. That is, there is no limit to the number of tasks that can be outstanding on a given engine. This greatly benefits the latency of execution, because network traffic can be hidden behind computation. However, this means that workload is assigned without knowledge of how long @@ -429,6 +429,11 @@ effect by setting hwm to a positive integer, 1 being maximum load-balancing (a task will never be waiting if there is an idle engine), and any larger number being a compromise between load-balance and latency-hiding. +In practice, some users have been confused by having this optimization on by +default, and the default value has been changed to 1. This can be slower, +but has more obvious behavior and won't result in assigning too many tasks to +some engines in heterogeneous cases. + Pure ZMQ Scheduler ------------------