Re: [Xen-devel] cap and reservation functionality in the credit2 scheduler?

[George Dunlap <george.dunlap@xxxxxxxxxx>]

On Wed, 2011-10-05 at 12:08 +0100, Eunbyung Park wrote:
> In addition, I found that adjusting dom0 weight have failed to work, 
> but 
> except for the dom0, it worked well.
> I found that this problem had been on xen-devel lists long time ago, but 
> it seems not to be solved yet.
> I think this may be related with spinlock. When I remove the 
> vcpu_schedule_lock_irq() in csched_dom_cntl(), it worked well.
> I'm not sure what is the real problem because I didn't completely 
> understand the mechanism about spinlocks in xen scheduler.

So I'm afraid that instead of telling you how the spinlocks are supposed
to work, I'm going to let you figure out what the locks should be doing
on your own. If you can't do that, then you may not be ready yet to work
on the scheduler.

I hope that doesn't sound too harsh, but the fact is that the scheduler
is probably one of the most deceptively simple parts of the Xen code.
It requires a lot of expertise to know even how to avoid race conditions
and deadlock, not to mention making a simple algorithm which has the
desired effects without undesirable side effects.  (The shadow code is
probably more complicated, for example, but it *looks* more complicated,
so people don't end up in over their head.)  I wouldn't be doing either
you or me a favor by encouraging you to work on something past your
capability level.

> 2011-10-05 ìí 7:24, George Dunlap ì ê:
> Actually, I don't have any idea in mind yet.
> however, I will try to devise a method to support them and make a patch.
> So, If you can afford to review, I will appreciate it :)

I'll be happy to review whatever you can send to the list. But like I
said above, beware of getting in over your head. :-)

> And, I think that there are still some to-do lists for the credit2 and 
> xl tools needs to include credit2 support.

This should be fairly straightforward to do, and would be much
appreciated!

 -George


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