Speaker
Charles Leggett
(Lawrence Berkeley National Lab. (US))
Description
In order to be able to make effective use of emerging hardware, where
the amount of memory available to any CPU is rapidly decreasing as
the core count continues to rise, ATLAS has begun a migration to a
concurrent, multi-threaded software framework, known as AthenaMT.
Significant progress has been made in implementing AthenaMT - we can
currently run realistic Geant4 simulations on massively concurrent
machines. the migration of realistic prototypes of
reconstruction workflows is more difficult, given the large amounts of
legacy code and the complexity and challenges of reconstruction
software. These types of workflows, however, are the types that will
most benefit from the memory reduction features of a multi-threaded
framework.
One of the challenges that we will report on in this paper is the
re-design and implementation of several key asynchronous technologies
whose behaviour is radically different in a concurrent environment
than in a serial one, namely the management of Conditions data and the
Detector Description, and the handling of asynchronous notifications
(such as FileOpen). Since asynchronous data, such as Conditions or
detector geometry, has a lifetime different than that of event data,
it cannot be kept in the Event Store. However, multiple instances of
the data need to be simultaneously accessible, such that concurrent
events that are, for example processing conditions data from different
validity intervals, can be executed concurrently in an efficient
manner with low memory overhead, and without multi-threaded conflicts.
