Re: [Xen-devel] RE: [Patch] Fix IDLE issue with sedf scheduler on IA64

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

On Jul 13, 2005, at 8:34 AM, Tian, Kevin wrote:

> > Magenheimer, Dan (HP Labs Fort Collins) wrote:
> >
> > Is there a better way (for ia64)?  I kind of like the solution
> > Keir and Ian imply... is it possible in context_switch to simply
> > "refuse" to switch to the idle domain?   E.g. if the idle domain
> > is the target of the switch, instead switch to domain0 (and
> > make it runnable)?
> This seems not easy to be simply done in context_switch without common
> change. Preventing switch to IDLE is easy, and a simple check in
> context_switch can achieve. However the really bad thing is about
> housekeep info within scheduler. Eg. domain0 may have been placed on
> waitq, with begin of next period still far away. Stealing slice of IDLE
> to Dom0 without notifying scheduler, may mess the future decision since
> next schedule will happen on Dom0's context and base on dom0's 
> statistic
> info...
See how x86 does this in context_switch() (arch/x86/domain.c). In 
particular, __context_switch is avoided for the idle domain, so the 
context restored is some register pops in ret_from_intr/restore_all_xen 
(arch/x86/x86_32/entry.S).
No scheduler changes or confusion necessary...

--
Hollis Blanchard
IBM Linux Technology Center


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