Re: [Xenomai] intel turbo boost

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On Wed, Nov 04, 2015 at 01:30:32AM +0100, Gilles Chanteperdrix wrote:
> On Thu, Sep 03, 2015 at 09:00:36AM +0200, Stéphane ANCELOT wrote:
> > Hi,
> > 
> > Do you think I can use the Intel integrated turbo boost mode, without 
> > problems.
> > 
> > I have this nice processor :
> > http://ark.intel.com/fr/products/76308/Intel-Core-i5-4300U-Processor-3M-Cache-up-to-2_90-GHz
> 
> Just experimented this, the turbo mode is a problem for applications
> which rely on a precise relation between the actual count of cpu
> cycles of a busy loop and the time. The sched_quota falls under that
> category and simply does not work reliably when turbo mode is
> enabled. Fortunately, it is possible to turn off turbo mode. For
> that, in the kernel configuration
> - enable CPU_FREQ
> - choose performance mode by default
> - enable intel pstate driver
> - echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo
> 
> Other than that, turbo mode does not seem to break the latency,
> which would mean that the tsc frequency does not change with turbo
> mode.

Turbo mode also breaks the autotune feature. So, on a machine with
turbo mode, autotune should be triggered after writing to the /proc
file.

-- 
					    Gilles.
https://click-hack.org