[Xen-ia64-devel] RE: [Xen-devel] RE: [Patch] Fix IDLE issue with sedf scheduler on IA64

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Magenheimer, Dan (HP Labs Fort Collins)
>[mailto:dan.magenheimer@xxxxxx]
>Sent: Thursday, July 14, 2005 11:52 PM
>
>> >I think domain0 only goes in the waitq at one point -- when
>> >it calls pal_halt_light to idle its virtual machine.  This
>> >case could be easily changed (there is already some code there)
>> >to ensure domain0 is always runnable.
>>
>> As I said in another mail, too many pal_halt_light in Dom0's
>> idle loop is even worse than current IDLE domain. (At lease
>> unmodified dom0 can't change that behavior)
>
>You misunderstand what I was suggesting:  When the hypervisor
>recognizes that a domain did a pal_halt_light:
>
>if (current == dom0) {
>       if (current is_the_only_non_idle_domain_on_the_run_queue) {
>               REAL_pal_halt_light;  // processor to low power state
>               return; // back to domain0
>      }
>      else do_sched_op(SCHEDOP_yield);
>}
>else do_sched_op(SCHEDOP_yield);
>
>Dan

Sounds good, and then you need help from scheduler to export that
important runqueue information. Also, for (current != dom0),
SCHEDOP_block is better than SCHEDOP_yield to emulate pal_halt_light...

Thanks,
Kevin

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