On Tue, 27 Oct 2026 02:50:45 GMT, Larry <[email protected]> wrote: >> ### Description >> >> The CRC32 kernel used on machines without AVX-512 >> (MacroAssembler::kernel_crc32) folds 512 bits of input per iteration, 128 >> bits per each of four parallel streams, but it reduces the final 128-bit >> state to 32 bits with the byte-wise table: two vpclmulqdq and a vpand fold >> the state down to 64 bits using the K_M_64 constant, and the rest is folded >> eight bits at a time with fold_8bit_crc32 - four folds on a 128-bit vector >> register, then four more on a general purpose register. >> >> Each 8-bit fold computes crc = T[crc & 0xFF] ^ (crc >> 8) and depends on the >> result of the previous fold, so the reduction is a serial chain of eight >> table lookups whose addresses depend on the incoming data, plus five >> XMM->GPR moves (four movdl to index the table, one to hand the value over to >> the GPR folds). >> >> This change replaces the reduction with the folding and Barrett sequence >> that kernel_crc32_avx512 already uses: >> - vpclmulqdq folds the 128-bit state down to 96 and then to 64 bits using >> the new K_128_64 constant; >> - a Barrett reduction with the new K_64_32 constant cancels the upper 32 >> bits with two carry-less multiplies; >> - pextrd extracts the CRC directly from the vector register; pextrd is >> SSE4.1 only, so it is guarded with VM_Version::supports_sse4_1() and falls >> back to vpsrldq + movdl; >> - the byte-wise table is still used by the prologue and for the trailing >> bytes, but not by the reduction anymore. >> >> K_128_64 and K_64_32 are added to _crc_by128_masks, following the naming and >> one-bit pre-shift conventions of the existing entries so that the table >> stays ordered by fold distance. K_M_64 was only used by the removed >> reduction and is dropped; the AOT address table is updated since the >> generated stub references the new entries. Only the non-AVX-512 CRC32 path >> changes: kernel_crc32_avx512 and CRC32C are untouched. >> >> ### TEST >> - env: Intel Xeon 6980P (Granite Rapids), single socket, 128 cores / 256 >> threads (SMT2), 3 NUMA nodes, 755 GiB RAM, Ubuntu 22.04.4 LTS, glibc 2.35 >> - JMH: test/micro/org/openjdk/bench/java/util/TestCRC32.java >> - jvmArgs: "-Xms4g -Xmx4g -XX:UseAVX=2" >> - results (ops/ms): >> | size | baseline | patched | delta | >> | ---: | ---: | ---: | ---: | >> | 16 | 23588.77 | 23589.00 | +0.0% | >> | 32 | 14586.33 | 19589.51 | +34.3% | >> | 64 | 13845.50 | 18218.98 | +31.6% | >> | 128 | 12564.96 | 16064.29 | +27.8% | >> | 256 | 12075.03 | 15205.08 | +25.9% | >> | 512 | 11147.73 | 13791.16 | +23.7% | >> | 1024 | 9623.2... > > Larry has updated the pull request incrementally with one additional commit > since the last revision: > > 8394259: Remove unused CRC32 helper
Good. I will submit our testing and let you know results before approval. ------------- PR Comment: https://git.openjdk.org/jdk/pull/33342#issuecomment-6445954746
