Refactor MPI communication

[greole]

This PR improves repartitioned multi gpu matrix values and vector value update performance.

[Copilot]

Pull Request Overview

This PR improves performance of repartitioned multi-GPU matrix values and vector value update operations by optimizing communication patterns and adding device communication initialization.

• Refactors all-to-all communication to use MPI operations (MPI_Igatherv, MPI_Iscatterv) for better performance
• Adds symmetric matrix optimization to skip redundant data transfers
• Introduces device communication initialization and repartitioned communicator support

Reviewed Changes

Copilot reviewed 9 out of 11 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/unit/MatrixWrapper/Distributed.cpp	Adds device communication initialization calls to test setup
src/StoppingCriterion.cpp	Adds timing measurements for performance analysis
src/MatrixWrapper/Distributed.cpp	Implements optimized MPI communication and symmetric matrix handling
src/CommunicationPattern.cpp	Adds new function for computing repartitioned all-to-all patterns
include/OGL/lduLduBase.hpp	Adds device communication initialization and timing code
include/OGL/StoppingCriterion.hpp	Adds frequency mode configuration for stopping criterion optimization
include/OGL/DevicePersistent/Vector.hpp	Replaces communication function with direct MPI calls for copy-back operation
include/OGL/DevicePersistent/ExecutorHandler.hpp	Adds rank management utilities and device communication setup
include/OGL/CommunicationPattern.hpp	Declares new repartitioned communication pattern function

Comments suppressed due to low confidence (1)

src/MatrixWrapper/Distributed.cpp:1

• Duplicate assignment to recv_offsets.back(). The first assignment on line 203 sets send_offsets.back() but the code incorrectly assigns to recv_offsets.back() twice. Line 203 should assign to send_offsets.back().

// SPDX-FileCopyrightText: 2024 OGL authors

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[Copilot]

The string concatenation is broken. Line 345 ends with a comment // + and line 346 is a separate statement that isn't assigned to anything. The + operator should be on line 345 to concatenate with line 346.

Suggested change

	std::string("\n\tRetrieve results bandwidth "); // +
	std::to_string(bandwidth_copy_back) + std::string(" [GByte/s]");
	std::string("\n\tRetrieve results bandwidth ") +
	std::to_string(bandwidth_copy_back) + std::string(" [GByte/s]");