linux-kernel - Re: [patch] CFS scheduler, -v8

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Date:	Thu, 03 May 2007 11:19:04 -0400
From:	Ting Yang <tingy@...umass.edu>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [patch] CFS scheduler, -v8


Srivatsa Vaddagiri wrote:
> On Thu, May 03, 2007 at 10:50:15AM +0200, Ingo Molnar wrote:
>  
>> - EEVDF concentrates on real-time (SCHED_RR-alike) workloads where they
>>   know the length of work units
>>     
>
> This is what I was thinking when I wrote earlier that EEVDF expects each
> task will specify "length of each new request"
> (http://lkml.org/lkml/2007/5/2/339).
>   
This is not very true based on my understanding of EEVDF, please look at 
the email I just sent out to Ingo for explanation.
> The other observation that I have of EEVDF is that it tries to be fair
> in the virtual time scale (each client will get 'wi' real units in 1
> virtual unit), whereas sometimes fairness in real-time scale also 
> matters?
> For ex: a multi-media app would call scheduler fair to it, it it recvs
> atleast 1 ms cpu time every 10 *real* milleseconds (frame-time). A rogue
> user (or workload) that does a fork bomb may skew this fairness for that
> multi-media app in real-time scale under EEVDF?
>   
First of all, CFS does not seems to address this issue to. This is a 
typical real-time or soft real-time question, that is not only the 
bandwidth of a task has to be fixed, i.e. 10% of cpu bandwidth (which 
proportional shared system, like CFS, EEVDF does not do), and the work 
need to satisfy a deadline.
In both CFS, EEVDF, the scheduler have keep tweaking weights to give a 
fixed bandwidth to application. Authors of EEVDF claims this can be 
done, but never implemented :-(

Ting
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