Post-graduate theses
Current Record: 59 of 833
|
Identifier |
000447836 |
Title |
Design and implementation of a write based version of the Exanet MPI |
Alternative Title |
Σχεδιασμός και υλοποίηση μιας έκδοσης του Exanest MPI βασισμένης σε εγγραφή |
Author
|
Νικολουδάκης, Μιχαήλ Β.
|
Thesis advisor
|
Πρατικάκης, Πολύβιος
|
Reviewer
|
Μαγκούτης, Κωνσταντίνος
Παπαευσταθίου, Βασίλειος
|
Abstract |
MPI is one of the leading communication protocols used in HPC (High Performance
Computing) suites today due to its portability and scalability. Many HPC applications
make use of MPI in order to enable communication between different processes. In
the scope of the ExaNeST project, an HPC prototype was deployed in the CARV
Laboratory of FORTH consisting of 512 ARMv8 cores coupled with FPGA logic. This
prototype makes use of special network primitives designed to allow the low latency
transmission of control messages as well as the efficient transfer of large data through
the Exanet network.
In order to exploit the aforementioned capabilities of the prototype, a highly
optimized MPI implementation (Exanet MPI) was developed in the scope of the same
project prior to our work. This implementation makes use of the prototype’s
communication primitives and manages to outperform the well known MPI
implementation, MPICH by achieving up to 30x lower latency. Exanet MPI supports
both an eager and a long communication protocol used for short and large MPI
transfers respectively. The long protocol depends on emulated DMA reads and
supports exclusively sender initiation.
Sender initiation is defined as the ability of the sender of an MPI message to initiate
the communication with the receiver by issuing an appropriate control message.
Despite its simplicity, sender initiation does not let us exploit scenarios in which the
receiver posts its request earlier than the sender. In addition, the use of emulated
reads requires the receiver to notify the sender about the end of a DMA transfer
through the use of an Ack control message which incurs extra latency.
In this thesis, we design and implement from scratch a write-based version of the
Exanet MPI that supports both sender and receiver initiation. With the use of DMA
writes, we render the sender able to determine the end of a DMA transfer by itself
without the need of acknowledgment from the receiver. Additionally, we take
advantage of cases where a receive request gets posted earlier than a matching send
request by letting the receiver initiate communication by asynchronously transferring
its DMA related information to the sender. Consequently, a sender that posts its send
request after the receiver, can immediately transfer data without the need of further
synchronization with the receiver. However, simply adding receiver initiation support
to the long protocol also infers some complications including (but not limited to) the
significant increase of the eager protocol's latency. We propose our method for
successfully facing the complications that arise from the support of receiver initiation
and we also further optimize the long protocol by eliminating the need of some
control messages. In order to break down the performance gain caused by our
optimizations we develop in total 4 variants of the write based Exanet MPI. In each
variant, we provide implementations for most point-to-point, collective as well as
communicator manipulating functions. We describe the use cases of each developed
variant and evaluate them against the already optimized read based original version
of Exanet MPI on the HPC prototype. We offer insight into the ways our control path
optimizations improve performance and the factors that let our implementation show
more benefit. For the evaluation we use both microbenchmarks and real scientific
applications. We show that our implementation can outperform the read based
protocol by up to 50% in communication latency while also reduce the total execution
time of specific applications by up to 10% (depending on the percentage of
communication time they contain).
|
Language |
English |
Subject |
Communication protocols |
|
Message passing interface |
|
Receiver initation |
|
Διεπαφή μεταβίβασης μηνυμάτων |
|
Πρωτόκολλα επικοινωνίας |
Issue date |
2022-07-29 |
Collection
|
School/Department--School of Sciences and Engineering--Department of Computer Science--Post-graduate theses
|
|
Type of Work--Post-graduate theses
|
Permanent Link |
https://elocus.lib.uoc.gr//dlib/0/5/c/metadata-dlib-1651729806-837841-26640.tkl
|
Views |
632 |