Kernel patch for more CPU families offers measurable speed increases

Question

I wanted to show folks a pretty nice patch that allows one more options when compiling a kernel for CPU families.  Complete list included at the bottom of this post.  I tested it using three different x86_64 machines running a generic x86-64 kernel and an otherwise identical kernel running with the optimized gcc options.
Conclusion: There are small but real speed increases using a make endpoint to building with this patch.
Details:
1) Three test machines: Intel Xeon X3360, Intel i7-2620M, Intel Core i7-3660K.
2) 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.
2a) X3360 = core2
2b) i7-2620M = corei7-avx
2c) i7-3660K = core-avx-i
3) Analyzed resulting distributions for statistical significance via ANOVA plots that clearly show statistically significant albeit small differences.
Discussion
1) 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).
2) 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:
core2       +87.5 ms
corei7-avx  +79.7 ms
core-avx-i  +257.2 ms
References:
Kernel patch: https://github.com/graysky2/kernel_gcc_patch
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_o … ion.txt.gz
Links to ANOVA plots:
Complete list of x86_64 CPU Families:
1. AMD Opteron/Athlon64/Hammer/K8 (MK8)
2. AMD 61xx/7x50/PhenomX3/X4/II/K10 (MAMDFAM10) (NEW)
3. AMD Barcelona (MBARCELONA) (NEW)
4. AMD Bobcat (MBOBCAT) (NEW)
5. AMD Bulldozer (MBULLDOZER) (NEW)
6. AMD Piledriver (MPILEDRIVER) (NEW)
7. Intel P4 / older Netburst based Xeon (MPSC)
8. Intel Core 2 (MCORE2)
9. Intel Core i7 (MCOREI7) (NEW)
11. Intel Core 2nd Gen AVX (MCOREI7AVX) (NEW)
12. Intel Core 3rd Gen AVX (MCOREAVXI) (NEW)
13. Intel Core AVX-2 (MCOREAVX2) (NEW)
14. Intel Atom (MATOM)
15. Generic-x86-64 (GENERIC_CPU)
Complete list of i686 CPU Families:
1. 386 (M386)
2. 486 (M486)
3. 586/K5/5x86/6x86/6x86MX (M586)
4. Pentium-Classic (M586TSC)
5. Pentium-MMX (M586MMX)
6. Pentium-Pro (M686)
7. Pentium-II/Celeron(pre-Coppermine) (MPENTIUMII)
8. Pentium-III/Celeron(Coppermine)/Pentium-III Xeon (MPENTIUMIII)
9. Pentium M (MPENTIUMM)
10. Pentium-4/Celeron(P4-based)/Pentium-4 M/older Xeon (MPENTIUM4)
11. AMD K6/K6-II/K6-III (MK6)
12. AMD Athlon/Duron/K7 (MK7)
13. AMD Opteron/Athlon64/Hammer/K8 (MK8)
14. AMD 61xx/7x50/PhenomX3/X4/II/K10 (MAMDFAM10) (NEW)
15. AMD Barcelona (MBARCELONA) (NEW)
16. AMD Bobcat (MBOBCAT) (NEW)
17. AMD Bulldozer (MBULLDOZER) (NEW)
18. AMD Piledriver (MPILEDRIVER) (NEW)
19. Crusoe (MCRUSOE)
20. Efficeon (MEFFICEON)
21. Winchip-C6 (MWINCHIPC6)
22. Winchip-2/Winchip-2A/Winchip-3 (MWINCHIP3D)
23. AMD Elan (MELAN)
24. GeodeGX1 (MGEODEGX1)
25. Geode GX/LX (MGEODE_LX)
26. CyrixIII/VIA-C3 (MCYRIXIII)
27. VIA C3-2 (Nehemiah) (MVIAC3_2)
28. VIA C7 (MVIAC7)
29. Intel Core 2 (MCORE2)
30. Intel Core i7 (MCOREI7) (NEW)
31. Intel Core 2nd Gen AVX (MCOREI7AVX) (NEW)
32. Intel Core 3rd Gen AVX (MCOREAVXI) (NEW)
33. Intel Core AVX-2 (MCOREAVX2) (NEW)
34. Intel Atom (MATOM)
Last edited by graysky (2013-01-16 19:14:09)

Answer 1

graysky wrote:Practically, why do you need more than a few frequencies?  For example, you're idle.  I would want the lowest freq.  You're under load.  I would want the highest frequency.  For situations in between, say launching a program, or moving data, whatever, an intermediate frequency would be fine.  What do you hope to achieve with a more refined list of available frequencies?
I agree, your CPU, in practice, is really either idle or loaded.
In my case (AMD 965, 4 freq steps) the processor is at lowest freq for about 90 - 95% of a time, and at highest for 5 - 10%. The 2 intermediate are used for about 0.1% of a time.
My guess would be that intermediate ones are only used for smooth transition from lowest to highest. So they really are hardware dependent...