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

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Date:	Wed, 02 May 2007 19:41:42 -0400
From:	Ting Yang <tingy@...umass.edu>
To:	vatsa@...ibm.com
CC:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [patch] CFS scheduler, -v8

Srivatsa Vaddagiri wrote:
> I briefly went thr' the paper and my impression is it expect each task
> to specify the length of each new request it initiates. Is that correct?
>   
No, the timeslice l_i here serves as a granularity control w.r.t 
responsiveness (or latency depends on how you interpret it). As wli said 
it can be express as a function of the priority, as we do for weight 
now. It is not related with the length of each new request. A request 
may be 1 seconds long, but the scheduler may still process it using 10ms 
timeslice. Smaller timeslice leads to more accuracy, i.e. closer to 
ideal case.
However, the maximum of timeslice l_i used by all active tasks 
determines the total responsiveness of the system, which I will explain 
in detail later.
> There is also p->wait_runtime which is taken into account when
> calculating p->fair_key. So if p3 had waiting in runqueue for long
> before, it can get to run quicker than 10ms later.
Consider if p3 is a newly started task or waked up task and carries no 
p->wait_runtime.

Ting
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