Re: [RFC v1] Tunable sched_mc_power_savings=n

[Balbir Singh <balbir@linux.vnet.ibm.com>]

Andi Kleen wrote:
> Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> writes:
>> The idea being proposed is to enhance the tunable with varied degrees
>> of consolidation that can work best for different workload
>> characteristics.  echo 2 > /sys/.../sched_mc_power_savings could
>> enable more aggressive consolidation than the default.
> 
> It would be better to fix the single power saving default to work
> better with bursty workloads too than to add more tunables. Tunables
> are basically "we give up, let's push the problem to the user"
> which is not nice. I suspect a lot of users won't even know if their
> workloads are bursty or not.  Or they might have workloads which
> are both bursty and not bursty.
> 
> Or did you try that and failed?
> 

A user could be an application and certain applications can predict their
workload. For example, a database, a file indexer, etc can predict their workload.

Policies are best known in user land and the best controlled from there.
Consider a case where the end user might select a performance based policy or a
policy to aggressively save power (during peak tariff times). With
virtualization, the whole concept of application is changing, the OS by itself
could be an application :)


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL