Re: [PATCH] xen/sched_credit: Use delay to control scheduling frequency

[George Dunlap <george.dunlap@citrix.com>]

On Tue, 2011-12-20 at 10:09 +0000, Dario Faggioli wrote:
> On Tue, 2011-12-20 at 17:44 +0800, Lv, Hui wrote: 
> > > It that constraint enforced anywhere?
> > 
> > Currently, it's not constraint enforced. 
> > I think George have gave the explanation in yesterday's discussion.
> > 
> I think that too, but maybe you can print some kind of warning when it
> happens?

I guess the consensus is that we should put in some effort to make the
interface more polished.

How about this:

First, add a ratelimit_us element to csched_priv, just like the current
tslice_ms element.

When the scheduler comes up (in csched_init), it checks to see if
MICROSECS(sched_ratelimit_us) > MILLISECS(sched_credit_tslice_ms); if
so, it prints a warning, and sets prv->ratelimit_us to
1000*prv->tslice_ms.

In the future, when we implement the domctls to change a scheduler's
ratelimit_us, and tslice_ms, we disallow changes which would violate the
"ratelimit < tslice" rule (returning -EINVAL or something like that).

Thoughts?

 -George