#Kernel_gcc_patch Kernel patch adds additional CPU options to the Linux kernel accessible under: Processor type and features ---> Processor family --->
Why a specific patch? The kernel uses its own set of CFLAGS, KCFLAGS. For exmaple, see:
- arch/x86/Makefile
- arch/x86/Makefile_32.cpu
- arch/x86/Kconfig.cpu
| CPU Family | GCC Optimization |
|---|---|
| Native optimizations autodetected by GCC | -march=native |
| AMD K10-family | -march=amdfam10 |
| AMD Family 10h (Barcelona) | -march=barcelona |
| AMD Family 14h (Bobcat) | -march=brver1 |
| AMD Family 15h (Bulldozer) | -march=bdver1 |
| Piledriver Family 15h (Piledriver) | -march=bdver2 |
| Intel 1st Gen Core i3/i5/i7-family (Nehalem) | -march=corei7 |
| Intel 2nd Gen Core i3/i5/i7-family (Sandybridge) | -march=corei7-avx |
| Intel 3rd Gen Core i3/i5/i7-family (Ivybridge) | -march=core-avx-i |
| Intel 4th Gen Core i3/i5/i7-family (Haswell) | -march=core-avx2 |
#Benchmarks ##Intro Three different machines running a generic x86-64 kernel and an otherwise identical kernel running with the optimized gcc options were tested using a make based endpoint.
##Conclusion There are small but real speed increases to running with this patch as judged by a make endpoint. The increases are on par with the speed increase that the upstream sanctioned core2 option gives users, so not including additional options seems somewhat arbitrary to me.
##Details
- Three test machines: Intel Xeon X3360, Intel i7-2620M, Intel Core i7-3660K.
- All ran the make benchmark (linked below) 35 times while booted into a 'generic' kernel. Then all ran the same make benchmark 35 times after booting into an optimized kernel. Below are the optimizations chosen for each machine.
- X3360 = core2
- i7-2620M = corei7-avx
- i7-3660K = core-avx-i
- Results were analyzed for statistical significance via ANOVA plots that clearly show statistically significant albeit small differences.
##Discussion
- All the assumptions for ANOVA are met:
- Data are normally distributed as show in the normal quantile plots.
- The population variances are fairly equal (Levene and Barlett tests).
- The ANOVA plots clearly show significance.
- Pair-wise analysis by Tukey-Kramer shows significance at the 0.05 level for all CPUs compared.
Below are the differences in median values:
| CPU | Difference in median value |
|---|---|
| core2 | +87.5 ms |
| core7-avx | +79.7 ms |
| core-avx-i | +257.2 ms |
##References
- Bash script that controls the benchmark: https://github.com/graysky2/bin/blob/master/bench
- Log file generated by script: http://repo-ck.com/bench/compile_time_optimization.txt.gz
##Credit
- Original author: jeroen AT linuxforge DOT net
- Link to original version: http://www.linuxforge.net/docs/linux/linux-gcc.php
##Data
###Corei7-avx vs. Generic
###Core-avx-i vs. Generic
###Core2 vs. Generic
