Color code: (critical, news during the meeting: green, news from this week: blue, news from last week: purple, no news: black)

EPN GPU Topics:

GPU Benchmarks in HS23 Contribution from ALICE

• Had a meeting last week, Gabriele will report on the status

Sync reconstruction

Async reconstruction

• Need to investigate short GPU stall problem.
• Limiting factor for pp workflow is now the TPC time series, which is to slow and creates backpressure (costs ~20% performance on EPNs). Enabled multi-threading as recommended by Matthias - need to check if it works.
• We can not set the GPU architectures to build fore in the environment variable field of Jenkins builds.
• Managed to run the o2-gpu-standalone-benchmark from an async build on CVMFS in the default GRID job container on the NERSC perlmutter site running on their A100 GPU.

GPU ROCm / compiler topics:

• Issues that disappeared but not yet understood: random server reboot with alma 9.4, miscompilation with ROCm 6.2, GPU getting stuck when DMA engine turned off, MI100 stalling with ROCm 5.5.
• Problem with building ONNXRuntime with MigraphX support, to be checked.
• Need to find a way to build ONNXRuntime with support for CUDA and for ROCm.
• Try to find a better solution for the problem with __device__ inline functions leaking symbols in the host code.
  
• LLVM Bump to 20.1: status?
• ROCm 6.4.1 status:
  • AMD is checking the reproducer. I have some idea how to narrow down where it miscompiles using different compile flags in per-kernel mode.
• Improved Standalone Benchmark CI, can now run RTC test for CUDA also with no GPU installed.
• Updating alidist/gpu-system to be build_requires only, and to generate a dummy modulefile (even if not used), as requested by Giulio.

TPC / GPU Processing 

• WIP: Use alignas() or find a better solution to fix alignment of monte carlo labels: https://its.cern.ch/jira/browse/O2-5314
• Waiting for TPC to fix bogus TPC transformations for good, then we can revert the workaround.
  
• Waiting for TPC to check PR which uses full cluster errors including average charge and occupancy map errors during seeding.
  
• Final solution: merging transformation maps on the fly into a single flat object: Draft version by Sergey exists but still WIP.
• Pending OpenCL2 issues:
  • printf not working due to confirmed bug in clang, fix is being prepared. Prevents further debugging for now.
    
  • Crash in merger, which can be worked around by disabling clang SPIRV optimization. Probably bug in clang, but need to fix printf first to debug.
    
  • Also with optimization disabled, crashing later in TPC merging, need printf to debug.
• Next high priority topic: Improvements for cluster sharing and cluster attachment at lower TPC pad rows.
• Need to check the problem with ONNX external memory allocator.