gluon-lds-opt

What problem does it solve?

Fix LDS (Local Data Share) bank conflicts in a Gluon GEMM kernel that loads tiles into shared memory via async_copy or buffer_load. Symptoms: high SQ_LDS_BANK_CONFLICT hardware counter, high-cycle s_waitcnt lgkmcnt(0) before MFMA in ATT traces, or ds_read instructions on the critical path in the amdgcn ISA. Two strategies: (1) swizzling — change SwizzledSharedLayout parameters from trivial (1,1,1) to bank-conflict-free (8,1,8); (2) padding — use PaddedSharedLayout with DistributedLinearLayout for global loads. Bank conflicts can reduce LDS throughput by 8–32x and dominate kernel runtime. Applies to both CDNA3 (gfx942) and CDNA4 (gfx950). Use /lds-bank-conflict to measure conflicts before and after. Trigger for any mention of LDS bank conflicts, ds_read stalls, lgkmcnt stalls, or SwizzledSharedLayout in a Gluon kernel.

Core Features & Use Cases

• Swizzle-based mitigation: convert trivial layouts to bank-conflict-free SwizzledSharedLayout parameters tuned for CDNA3/4.
• Padding-based mitigation: switch to DistributedLinearLayout + PaddedSharedLayout to explicitly control data placement.
• Profiling guidance: measure SQ_LDS_BANK_CONFLICT with /kernel-perf-analysis and inspect ATT traces for ds_read stalls.

Quick Start

Apply bank-conflict-free SwizzledSharedLayout settings (e.g., SwizzledSharedLayout(8, 2, 8, order=[1, 0])) to your Gluon GEMM tiles and profile the LDS performance.