mirror of
https://sourceware.org/git/glibc.git
synced 2024-12-29 05:51:10 +00:00
5bf0ab8057
Previously we use `rep stosb` for all medium/large memsets. This is notably worse than non-temporal stores for large (above a few MBs) memsets. See: https://docs.google.com/spreadsheets/d/1opzukzvum4n6-RUVHTGddV6RjAEil4P2uMjjQGLbLcU/edit?usp=sharing For data using different stategies for large memset on ICX and SKX. Using non-temporal stores can be up to 3x faster on ICX and 2x faster on SKX. Historically, these numbers would not have been so good because of the zero-over-zero writeback optimization that `rep stosb` is able to do. But, the zero-over-zero writeback optimization has been removed as a potential side-channel attack, so there is no longer any good reason to only rely on `rep stosb` for large memsets. On the flip size, non-temporal writes can avoid data in their RFO requests saving memory bandwidth. All of the other changes to the file are to re-organize the code-blocks to maintain "good" alignment given the new code added in the `L(stosb_local)` case. The results from running the GLIBC memset benchmarks on TGL-client for N=20 runs: Geometric Mean across the suite New / Old EXEX256: 0.979 Geometric Mean across the suite New / Old EXEX512: 0.979 Geometric Mean across the suite New / Old AVX2 : 0.986 Geometric Mean across the suite New / Old SSE2 : 0.979 Most of the cases are essentially unchanged, this is mostly to show that adding the non-temporal case didn't add any regressions to the other cases. The results on the memset-large benchmark suite on TGL-client for N=20 runs: Geometric Mean across the suite New / Old EXEX256: 0.926 Geometric Mean across the suite New / Old EXEX512: 0.925 Geometric Mean across the suite New / Old AVX2 : 0.928 Geometric Mean across the suite New / Old SSE2 : 0.924 So roughly a 7.5% speedup. This is lower than what we see on servers (likely because clients typically have faster single-core bandwidth so saving bandwidth on RFOs is less impactful), but still advantageous. Full test-suite passes on x86_64 w/ and w/o multiarch. Reviewed-by: H.J. Lu <hjl.tools@gmail.com> |
||
|---|---|---|
| .. | ||
| aarch64 | ||
| alpha | ||
| arc | ||
| arm | ||
| csky | ||
| generic | ||
| gnu | ||
| hppa | ||
| htl | ||
| hurd | ||
| i386 | ||
| ieee754 | ||
| loongarch | ||
| m68k | ||
| mach | ||
| microblaze | ||
| mips | ||
| nios2 | ||
| nptl | ||
| or1k | ||
| posix | ||
| powerpc | ||
| pthread | ||
| riscv | ||
| s390 | ||
| sh | ||
| sparc | ||
| unix | ||
| wordsize-32 | ||
| wordsize-64 | ||
| x86 | ||
| x86_64 | ||