Re: [Xenomai] latency spikes under load

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

On 12/11/2013 05:04 PM, Tobias Luksch wrote:
>>> On Wed, Dec 11, 2013 at 02:23:38PM +0000, Kurijn Buys wrote: I
>>> enabled APIC, and the latency peaks at 16us only now, and even
>>> less with
>> load.
>>> This also had an effect on my analogy problem, but not
>>> completely... I will
>> start a new thread for that...
>>
>> If your latency drops under loads, it sounds as if your CPU is
>> slowing down when idle and taking a while to speed back up.
>> Perhaps changing the CPU governer to performance or user controlled
>> and setting a fixed CPU speed would keep the latency low all the
>> time (although at the cost of more power consumption).
>
> I had a similar problem where the latency behavior changed depending
> on the CPU load on an Intel CPU (see " Problems with running Xenomai
> on Core i5" thread of this list). It turned out to be a C1E "feature"
> that I could not influence in the BIOS. But clearing the second bit
> of the MSR_IA32_POWER_CTL register did help. I used the wrmsr command
> of the msr-tools package.

Ok, we could integrate this C1E workaround as the SMI workaround or AMD 
C1E workaround. Do you have any pointer, which would explain me a way to 
detect that this MSR is available (and C1E is enabled, but I guess it is 
just a matter of reading the MSR). Second question is: has not this 
change any repercussion on processor temperature.

-- 
					    Gilles.