On Wed, Feb 12, 2025 at 09:02:27PM +0000, Devulapalli, Raghuveer wrote: > Also, do we really need to have both USE_SSE42_CRC32C and > USE_SSE42_CRC32C_WITH_RUNTIME_CHECK > features support? The former macro is used to enable running the SSE42 > version without a runtime check > when someone builds with -msse4.2. The code looks fine now, but the runtime > dispatch rules get complicated > as we add the PCLMUL and AVX512 dispatch in the future. IMO, this additional > complexity is not worth it. > The cpuid runtime dispatch runs just once when postgres server is first setup > and would hardly affect performance. > Let me know what you think.
I think the idea behind USE_SSE42_CRC32C is to avoid the function pointer overhead if possible. I looked at switching to always using runtime checks for this stuff, and we concluded that we'd better not [0]. [0] https://postgr.es/m/flat/20231030161706.GA3011%40nathanxps13 -- nathan
