This 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:
|CPU Family||GCC Optimization|
|Native optimizations autodetected by GCC||-march=native|
|AMD Improved K8-family||-march=k8-sse3|
|AMD Family 10h (Barcelona)||-march=barcelona|
|AMD Family 14h (Bobcat)||-march=btver1|
|AMD Family 15h (Bulldozer)||-march=bdver1|
|AMD Piledriver Family 15h (Piledriver)||-march=bdver2|
|AMD Steamroller Family 15h 30h-3fh models (Steamroller)||-march=bdver3|
|AMD Family 16h (Jaguar)||-march=btver2|
|Intel Silvermont family of low-power Atom processors (Silvermont)||-march=silvermont|
|Intel 1st Gen Core i3/i5/i7-family (Nehalem)||-march=nehalem|
|Intel 1.5 Gen Core i3/i5/i7-family (Westmere)||-march=westmere|
|Intel 2nd Gen Core i3/i5/i7-family (Sandybridge)||-march=sandybridge|
|Intel 3rd Gen Core i3/i5/i7-family (Ivybridge)||-march=ivybridge|
|Intel 4th Gen Core i3/i5/i7-family (Haswell)||-march=haswell|
|Intel 5th Gen Core i3/i5/i7-family (Broadwell)||-march=broadwell|
|Intel 6th Gen Core i3/i5/i7-family (Skylake)||-march=skylake|
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.
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.
- 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 = sandybridge
- i7-3660K = ivybridge
- Results were analyzed for statistical significance via ANOVA plots that clearly show statistically significant albeit small differences.
- 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|
- 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
- Original author: jeroen AT linuxforge DOT net
- Link to original version: http://www.linuxforge.net/docs/linux/linux-gcc.php
Find support for older version of the linux kernel and of gcc in the outdated_versions directory.