[Xenomai] intel turbo boost

[Xenomai] intel turbo boost

[Stéphane ANCELOT]

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

Regards,
S.Ancelto

Re: [Xenomai] intel turbo boost

[Gilles Chanteperdrix]

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.


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

Re: [Xenomai] intel turbo boost

[Gilles Chanteperdrix]

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

Re: [Xenomai] intel turbo boost

[Stéphane ANCELOT]

On 08/11/2015 12:26, Gilles Chanteperdrix wrote:
> 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.
>
Hi,
You can disable turbo mode, in bios cpu settings . Writting to the 
no_turbo file is not permitted, but equals 1.
How do you trig autotune ?
Regards,
Steph

Re: [Xenomai] intel turbo boost

[Philippe Gerum]

On 11/12/2015 09:20 AM, Stéphane ANCELOT wrote:
> On 08/11/2015 12:26, Gilles Chanteperdrix wrote:
>> 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.
>>
> Hi,
> You can disable turbo mode, in bios cpu settings . Writting to the
> no_turbo file is not permitted, but equals 1.
> How do you trig autotune ?

http://www.xenomai.org/documentation/xenomai-3/html/man1/autotune/index.html

The calibration obtained might be conservative in some cases, autotune
is aimed at suggesting sane and efficient values. You can still refine
the results via the /proc/xenomai/clock/coreclk interface if need be.

-- 
Philippe.