[Xenomai] Low-latency desktop setting

[Xenomai] Low-latency desktop setting

[Yogi A. Patel]

In configuring the kernel (after patching with xenomai), there is an option to change the preemption model to "low-latency desktop".

Is this a setting that should be set? Or should it be left to the default preemption mode??

How does this setting affect the real-time performance of a xenomai enabled kernel?

--
Yogi A. Patel
(828) 291.6715
yapatel.org | @yapatel525

Re: [Xenomai] Low-latency desktop setting

[Gilles Chanteperdrix]

On 08/28/2014 09:49 PM, Yogi A. Patel wrote:
> In configuring the kernel (after patching with xenomai), there is an
> option to change the preemption model to "low-latency desktop".
> 
> Is this a setting that should be set? Or should it be left to the
> default preemption mode??
> 
> How does this setting affect the real-time performance of a xenomai
> enabled kernel?

This option is about Linux preemption, it affects how often Linux is
willing to preempt itself, in the throughput/latency fight, it gives
advantage to (Linux) latency at the expense of througput. It does not
affect Xenomai directly, but rather indirectly: it creates a code with a
lower "density", by littering the Linux kernel execution with checks for
the need of rescheduling, so that Linux has a larger pollution effect on
caches. In my experience, you get slightly lower Linux latencies by
turning CONFIG_PREEMPT off (selecting CONFIG_PREEMPT_NONE).

-- 
                                                                Gilles.

Re: [Xenomai] Low-latency desktop setting

[Gilles Chanteperdrix]

On 08/28/2014 10:02 PM, Gilles Chanteperdrix wrote:
> On 08/28/2014 09:49 PM, Yogi A. Patel wrote:
>> In configuring the kernel (after patching with xenomai), there is an
>> option to change the preemption model to "low-latency desktop".
>>
>> Is this a setting that should be set? Or should it be left to the
>> default preemption mode??
>>
>> How does this setting affect the real-time performance of a xenomai
>> enabled kernel?
> 
> This option is about Linux preemption, it affects how often Linux is
> willing to preempt itself, in the throughput/latency fight, it gives
> advantage to (Linux) latency at the expense of througput. It does not
> affect Xenomai directly, but rather indirectly: it creates a code with a
> lower "density", by littering the Linux kernel execution with checks for
> the need of rescheduling, so that Linux has a larger pollution effect on
> caches. In my experience, you get slightly lower Linux latencies by
> turning CONFIG_PREEMPT off (selecting CONFIG_PREEMPT_NONE).
> 

I meant you get lower XENOMAI latencies by turning it off. Of course you
get higher Linux latencies.


-- 
                                                                Gilles.