Re: [patch] CFS scheduler, -v8

Ting Yang
2007-05-03T15:19:13Z

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