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

To: "Hollis Blanchard" <hollisb@xxxxxxxxxx>
Subject: RE: [Xen-devel] RE: [Patch] Fix IDLE issue with sedf scheduler on IA64
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Thu, 14 Jul 2005 09:02:25 +0800
Cc: "Magenheimer, Dan \(HP Labs Fort Collins\)" <dan.magenheimer@xxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
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Thread-topic: [Xen-devel] RE: [Patch] Fix IDLE issue with sedf scheduler on IA64
>From: Hollis Blanchard [mailto:hollisb@xxxxxxxxxx]
>Sent: Wednesday, July 13, 2005 10:32 PM
>On Jul 13, 2005, at 8:34 AM, Tian, Kevin wrote:
>> This seems not easy to be simply done in context_switch without
>> 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
>> to Dom0 without notifying scheduler, may mess the future decision
>> 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
>No scheduler changes or confusion necessary...

What you talked is about the optimization which is the neat way I
prefer, just like Ian suggested to use concept of lazy context switch
instead of eliminating IDLE domain earlier.

But this is not the same point as what Dan is suggesting. Dan is
suggesting to remove IDLE completely, or get IDLE simply an alias for
Dom0. My concern was just raised upon that direction - difficult to
prevent scheduling IDLE (not mean optimization for context switch)
without common scheduler change...


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