[LAU] Basic question about use of a lowlatency kernel

[david]

On 02/18/2013 01:42 PM, Ralf Mardorf wrote:
> On Mon, 18 Feb 2013 23:59:30 +0100, Len Ovens <len at ovenwerks.net> wrote:
>> On Mon, February 18, 2013 12:36 pm, jonetsu at teksavvy.com wrote:
>>> If a better response time from the kernel is something that's Good, why
>>> isn't lowlatency kernels a default in Linux distros (well, at least in
>>> Linux Mint and Fedora)  If it is So Good, what are the arguments for not
>>> having a lowlatency kernel by default ?  Any drawbacks ?  I presume the
>>> Audio-oriented Linux distros do have lowlatency kernels by default, do
>>> they ?
>>
>> low latency does not equal performance.
>> low latency and high throughput are not the same either.
>>
>> Low latency means servicing an audio device more often, complete with the
>> overhead involved in that. It means prioritizing one set of RT/lowlatency
>> processes over others for a set purpose. when running audio at a low
>> latency, the rest of my desktop slows down a lot to make sure my audio
>> does not glitch.
>>
>> Low latency is a different set of priorities than performance.
>
> Performance for _my_ averaged non-audio desktop usage isn't less good,
> when using a kernel-rt or full preempt kernel with threadirqs set, than
> when using a vanilla or so called desktop optimized kernel, so I'm
> usually using a self compiled kernel-rt. However, I'm seldom toying
> around with my computer, so "averaged non-audio" does mean that I use
> mail clients, browsers and GIMP, even for consuming multimedia, I seldom
> use the computer.
>
> But making the kernel-rt a default, would be as bad, as making flashy
> animated 3D desktops a default, so IMO distros should stop this desktop
> insanity, but keep non-rt-kernels, while providing a kernel-rt by the
> repositories.

I understand another argument against making an RT kernel the default 
stock one is that a runaway RT process could produce an internal 
denial-of-service condition. IIRC, the thought was that people who 
actually needed an RT kernel knew about the risk and would accept it, 
while ordinary people who don't need RT don't have to encounter it.

Vague recollection from something read somewhere, I think it was a 
discussion list archive I found on the web somewhere.

-- 
David
gnome at hawaii.rr.com
authenticity, honesty, community
http://clanjones.org/david/
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