RE: [Xen-devel] [PATCH] Add migration_cost option to scheduler

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

>From: George Dunlap
>Sent: Monday, March 09, 2009 8:56 PM
>
>Hmm, I think this patch may not be exactly what we want.  It looks
>like it checks for how long a vcpu has been in its current stat, not
>how recently it has been running.  So if a vcpu sleeps for a long time
>on a cpu that's running other workloads, then wakes up
>(blocked->runnable), the cache is by no means "hot".  But since it has
>only been in the "runnable" state for a few hundred cycles, it won't
>be migrated, even though there's little cost.

Then to add a per-vcpu last_running_timestamp which is recorded when 
vcpu is scheduled out, could hit the purpose here?

>
>However, if the pcpu was idle since the last time this vcpu ran (i.e.,
>if we're just catching the vcpu in the process of waking up), the
>cache *is* still hot.  Hmm....
>

If peer pcpu is idle, shouldn't it be skipped by load balancer running on
another pcpu, which is out of the cache-hot logic?

Thanks,
Kevin
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