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

["Yang, Xiaowei" <xiaowei.yang@xxxxxxxxx>]

Tian, Kevin wrote:
> > 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?
Yes, it's more reasonable. I can make a patch.

Thanks,
xiaowei

> > 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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