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GGitHub[libc][gpu] Disable loop unrolling in the throughput benchmark loop (#153971)

75bf7392创建于 2025年8月17日历史提交

文件	最后提交记录	最后更新时间
CMakeLists.txt	[libc] Polish GPU benchmarking (#153900) This patch provides cleanups and improvements for the GPU benchmarking infrastructure. The key changes are: - Fix benchmark convergence bug: Round up the scaled iteration count (ceil) to ensure it grows properly. The previous truncation logic causes the iteration count to get stuck. - Resolve remaining compiler warning. - Remove unused BenchmarkLogger files: This is dead code that added maintenance and cognitive overhead without providing functionality. - Improve build hygiene: Clean up headers and CMake dependencies to strictly follow the 'include what you use' (IWYU) principle.	11 个月前
timing.h	[libc][gpu] Disable loop unrolling in the throughput benchmark loop (#153971) This patch makes GPU throughput benchmark results more comparable across targets by disabling loop unrolling in the benchmark loop. Motivation: * PTX (post-LTO) evidence on NVPTX: for libc sin, the generated PTX shows the throughput loop unrolled 8x at N=128 (one iteration advances the input pointer by 64 bytes = 8 doubles), interleaving eight independent chains before the back-edge. This hides latency and significantly reduces cycles/call as the batch size N grows. * Observed scaling (NVPTX measurements): with unrolling enabled, sin dropped from ~3,100 cycles/call at N=1 to ~360 at N=128. After enforcing #pragma clang loop unroll(disable), results stabilized (e.g., from ~3100 cycles/call at N=1 to ~2700 at N=128). * libdevice contrast: the libdevice sin path did not exhibit a similar drop in our measurements, and the PTX appears as compact internal calls rather than a long FMA chain, leaving less ILP for the outer loop to extract. What this change does: * Applies #pragma clang loop unroll(disable) to the GPU throughput() loop in both NVPTX and AMDGPU backends. Leaving unrolling entirely to the optimizer makes apples-to-apples comparisons uneven (e.g., libc vs. vendor). Disabling unrolling yields fairer, more consistent numbers.	11 个月前