Scheduler queues for less os-jitter?

Scheduler queues for less os-jitter?

[Uwaysi Bin Kareem]

I was just wondering, have you considered this?

If daemons are contributing to os-jitter, wouldn`t having them all on  
their own queue reduce jitter? So people could have the stuff like in  
Ubuntu they want, without affecting jitter, or needing stuff like Tiny  
Core, for tiny jitter?

So you get (simplified) something like mainapp - process1 in queue 2,  
mainapp - process2 in queue 2, mainapp - process 3 in queue 2, etc.

Or is that already batch maybe, lol.

Peace Be With You.

Re: Scheduler queues for less os-jitter?

[Mike Galbraith]

On Wed, 2012-10-10 at 20:13 +0200, Uwaysi Bin Kareem wrote: 
> I was just wondering, have you considered this?
> 
> If daemons are contributing to os-jitter, wouldn`t having them all on  
> their own queue reduce jitter? So people could have the stuff like in  
> Ubuntu they want, without affecting jitter, or needing stuff like Tiny  
> Core, for tiny jitter?
> 
> So you get (simplified) something like mainapp - process1 in queue 2,  
> mainapp - process2 in queue 2, mainapp - process 3 in queue 2, etc.
> 
> Or is that already batch maybe, lol.

You could try SCHED_AUTOGROUP, or create whatever task groups manually,
or use systemd to do that for you.  Like everything else having anything
to do with scheduling, all are double edged swords, so may help, may
hurt.

-Mike

Fwd: Re: Scheduler queues for less os-jitter?

[Uwaysi Bin Kareem]

------- Forwarded message -------
From: "Uwaysi Bin Kareem" <uwaysi.bin.kareem@paradoxuncreated.com>
To: "Mike Galbraith" <efault@gmx.de>
Cc:
Subject: Re: Scheduler queues for less os-jitter?
Date: Sun, 04 Nov 2012 02:19:39 +0100

On Thu, 11 Oct 2012 04:46:34 +0200, Mike Galbraith <efault@gmx.de> wrote:

> On Wed, 2012-10-10 at 20:13 +0200, Uwaysi Bin Kareem wrote:
>> I was just wondering, have you considered this?
>>
>> If daemons are contributing to os-jitter, wouldn`t having them all on
>> their own queue reduce jitter? So people could have the stuff like in
>> Ubuntu they want, without affecting jitter, or needing stuff like Tiny
>> Core, for tiny jitter?
>>
>> So you get (simplified) something like mainapp - process1 in queue 2,
>> mainapp - process2 in queue 2, mainapp - process 3 in queue 2, etc.
>>
>> Or is that already batch maybe, lol.
>
> You could try SCHED_AUTOGROUP, or create whatever task groups manually,
> or use systemd to do that for you.  Like everything else having anything
> to do with scheduling, all are double edged swords, so may help, may
> hurt.
>
> -Mike
>

Actually I did achieve this with fifo-relatime. Low jitter OpenGL seems to
be able to do, running the opengl app as realtime, with a low
sched_rt_period_us value and a high sched_rt_runtime_us value.

Peace Be With You.

Re: Scheduler queues for less os-jitter?

[Uwaysi Bin Kareem]

Ok, anyway realtime processes did not work quite as expected.  
("overloaded" machine, even though cpu-time is only 10%). So I guess I  
have to enable cgroups and live with the overhead then.

If I set cpu-limits there, does that involve an absolute value, or is it  
normalized, so that even if I do 0.001% cpu for processes, they get all  
cpu, when there is nothing running?

Peace Be With You.

Re: Scheduler queues for less os-jitter?

[Mike Galbraith]

On Sun, 2012-11-04 at 10:20 +0100, Uwaysi Bin Kareem wrote: 
> Ok, anyway realtime processes did not work quite as expected.  
> ("overloaded" machine, even though cpu-time is only 10%). So I guess I  
> have to enable cgroups and live with the overhead then.
> 
> If I set cpu-limits there, does that involve an absolute value, or is it  
> normalized, so that even if I do 0.001% cpu for processes, they get all  
> cpu, when there is nothing running?

See Documentation/cgroups.  Between cgroups, cpusets, scheduler classes
and priorities, you have heaping truckloads of control over what runs
where and when.  The missing element in your low jitter quest is a
desktop and applications that were written for realtime performance.

-Mike