Re: [PATCH] Add migration_cost option to scheduler

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

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