Explain GPU Register Spills and Their Performance Cost
AMDSoftware Engineer · OnsiteLast updated
Explain GPU register spills through live-variable pressure, compiler allocation, spill traffic, occupancy tradeoffs, and measured optimization choices.
What is a register spill in a GPU kernel, why does it happen, and how would you determine whether it is hurting performance?
Constraints & Assumptions
Discuss compiler-managed per-thread registers and the storage used when values cannot remain in registers. Do not confuse a spill with explicitly declared shared/local scratchpad memory; terminology differs across programming systems.
Clarifying Questions
What is the kernel's register usage and live-variable pressure? Is occupancy limited by registers? Does the compiler report spills? What memory traffic and stalls appear in profiling?
Follow-up questions
- Can forcing a lower register limit make a kernel slower? How can unrolling or large local arrays affect pressure? When might recomputation be cheaper than preserving a value?
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