Re: [RFC][PATCH] Make MAX_RT_PRIO and MAX_USER_RT_PRIO configurable

["K.R. Foley" <kr@cybsft.com>]

Esben Nielsen wrote:
> On Wed, 27 Jul 2005, Ingo Molnar wrote:
> 
> 
>>* Steven Rostedt <rostedt@goodmis.org> wrote:
>>
>>
>>>Perfectly understood.  I've had two customers ask me to increase the 
>>>priorities for them, but those where custom kernels, and a config 
>>>option wasn't necessary. But since I've had customers asking, I 
>>>thought that this might be something that others want.  But I deal 
>>>with a niche market, and what my customers want might not be what 
>>>everyone wants. (hence the RFC in the subject).
>>>
>>>So if there are others out there that would prefer to change their 
>>>priority ranges, speak now otherwise this patch will go by the waste 
>>>side.
>>
>>i'm not excluding that this will become necessary in the future. We 
>>should also add the safety check to sched.h - all i'm suggesting is to 
>>not make it a .config option just now, because that tends to be fiddled 
>>with.
>>
> 
> Isn't there a way to mark it "warning! warning! dangerous!" ?
> 
> Anyway: I think 100 RT priorities is way overkill - and slowing things
> down by making the scheduler checking more empty slots in the runqueue.
> Default ought to be 10. In practise it will be very hard to have
> a task at the lower RT priority behaving real-time with 99 higher
> priority tasks around. I find it hard to believe that somebody has an RT
> app needing more than 10 priorities and can't do with RR or FIFO
> scheduling within a fewer number of prorities.
> 
> Esben
> 

Actually, is it really that slow to search a bitmap for a slot that 
needs processing? I work on real-time test stands which are less of an 
embedded system and more of a real Unix system that require determinism. 
It is very nice in some cases to have more than 10 RT priorities to work 
with.

-- 
    kr