GDR D2H much slower than H2D and cudaMemcpy
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 25/100
- Issue type
- Bug
- Clarity
- Needs clarification
- Activity status
- Stale
- Tech stack
- c
- Domain
- performance
Research direction
Begin by reproducing the reported copy_bw measurements on an A100 SXM and compare H2D and D2H with cuMemcpy across transfer sizes. Done means identifying and documenting why large H2D transfers stall near 20 GB/s and why D2H remains slower; the issue names no source files or tests.
Written by the indexing model from the issue text.
Description
Problem: When I test copy_bw on A100 SXM，I noticed some issue that need some help on explaination:
- H2D is persistently faster than cuMemcpy in small data size as expected, while for large data size it fails to grow when reaches 20GB/s. What is the reason for this degradation?
- D2H is much slower than H2D and never reaches high bandwidth even when data size is large enough. I guess the reason for the first phenomenon is that CPU need another dispatch trip to let GPU starts D2H, while I have no idea for the second one.
Anyone could help with the above questions?
- Dominant language
- C
- Stars
- 1.4k
- Forks
- 198
- PR merge metrics
- No merged PRs in 30d
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