[Beowulf] Turboboost/IDA on Nehalem

[Peter Kjellstrom]

On Friday 18 June 2010, Hearns, John wrote:
> Does anyone know much about Turboboost on Nehalem?
> I would like to have some indication that this is working, and perhaps
> measure what effect it has.
> I have enabled Turboboost in the BIOS, however when I modprobe
> acpi_cpufreq I get
>
> FATAL: Error inserting acpi_cpufreq
> (/lib/modules/2.6.31.12-0.2-desktop/kernel/arch/x86/kernel/cpu/cpufreq/a
> cpi-cpufreq.ko): No such device

On stock CentOS-5 it looks like this (with dual E5520):
 [root at m1 ~]# uname -r
 2.6.18-194.3.1.el5
 [root at m1 ~]# /etc/init.d/cpuspeed start
 Enabling ondemand cpu frequency scaling:                   [  OK  ]
 [root at m1 ~]# lsmod | grep acpi_cpufreq
 acpi_cpufreq           47937  0
 [root at m1 ~]# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
 2268000 2267000 2133000 2000000 1867000 1733000 1600000

Turbo-boost is the +1MHz freq 2268000. When the governor goes looking for the
highest available frequency the CPU goes into turbo-mode. The actual
frequency then is determined by available power and thermal margins but
ultimately limited depending on processor model (my E5520 can do one freq.
step, that is, 2.26 -> 2.4 GHz. X55xx can do two).

In my experience (E5520 and X5550) turbo mode works and gives you extra
performance even when using all cores (HPC load). However, power consumption
typically goes up a lot.

/Peter
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