Re: [RFD] sched/deadline: EDF dynamic quota design

[xiaofeng.yan]

On 2014/6/17 16:01, Luca Abeni wrote:
> Hi,
>
> On 06/17/2014 04:43 AM, xiaofeng.yan wrote:
> [...]
> > > The basic ideas are (warning! This is an over-simplification of the 
> > > algorithm! :)
> > > - You assign runtime and period to each SCHED_DEADLINE task as usual
> > > - Each task is guaranteed to receive its runtime every period
> > > - You can also define a maximum fraction Umax of the CPU time that the
> > >   SCHED_DEADLINE tasks can use. Note that Umax _must_ be larger or 
> > > equal
> > >   than sum_i runtime_i / period_i
> > >   (note: in the original GRUB paper, only one CPU is considered, and 
> > > Umax is
> > >   set equal to 1)
> > > - If the tasks are consuming less than Umax, then the scheduling 
> > > algorithm
> > >   allows them to use more runtime (but not less than the guaranteed 
> > > runtime_i)
> > >   in order to use up to Umax.
> > >   This is achieved by modifying the rule used to decrease the 
> > > runtime: in
> > >   SCHED_DEADLINE, if a task executes for a time delta, its runtime 
> > > is decreased
> > >   by delta; using GRUB, it would be decreased by a smaller amount of 
> > > time
> > >   (computed based on Umax, on the active SCHED_DEADLINE tasks, etc...).
> > >   This requires to implement some kind of state machine (the details 
> > > are in
> > >   the GRUB paper)
> > >
> > > I also had an implementation of the GRUB algorithm (based on a 
> > > modification
> > > of my old CBS scheduler for Linux), but the computational complexity 
> > > of the
> > > algorithm was too high. That's why I never proposed to merge it in 
> > > SCHED_DEADLINE.
> > > But maybe there can be some trade-off between the "exact compliance 
> > > with the
> > > GRUB algorithm" and implementation efficiency that can make it 
> > > acceptable...
> > Has these  codes been opened about the implementation in some 
> > community or not ?
> The old GRUB scheduler for Linux was used for some experiments 
> published in a paper
> at RTLWS 2007, and of course the code was open-source (released under 
> GPL).
> It required a patch for the Linux kernel (I used a 2.6.something 
> kernel) which allowed
> to load the scheduler as a kernel module (yes, I know this is the 
> wrong way to go...
> But implementing it like this was simpler :).
> That is very old code... I probably still have it somewhere, but I 
> have to search
> for it. If someone is interested, I can try to search (the story of 
> the user-space
> daemon for adaptive reservations is similar: I released it as 
> open-source years ago...
> If anyone is interested I can search for this code too)
>
>
>                 Luca
I'm glad that you reply this email.  yes, I'm so interesting about your 
solution.  In fact , there are scenarios
in our product.  Could you send me a link if you have?  I can test your 
solution in our scene if you like.

Thanks
Yan
>


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