Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken

* Arjan van de Ven [off-list ref] wrote:

On 1/10/2012 1:18 AM, Ingo Molnar wrote:

quoted

* Suresh Siddha [off-list ref] wrote:

quoted

On Tue, 2012-01-10 at 00:58 -0500, Youquan Song wrote:

quoted

Thanks Peter! Here is the patch. 

Youquan, As far as I know both the
sched_smt_power_savings/sched_mc_power_savings are broken for atleast an
year.

We want a single knob, sched_power_savings - with the mc_ and 
smt_ ones still kept and aliased to sched_power_savings, for 
compatibility reasons.

As Peter said, the other reasonable option is to have no knob at 
all and restart this code from scratch.

The other thing we should do is to add sane defaults: to turn on 
sched_power_savings *AUTOMATICALLY* when a system is obviously 
battery driven and turn it off when the system is obviously AC 
driven. User-space can still implement policy and override the 
kernel's default, but there's absolutely no excuse to not offer 
this default ourselves.

a very good default would be to keep all tasks on one package 
until half the cores in the package are busy, and then start 
spreading out.

I suspect that'll be the 90% case coverage.

Maybe - but there's no reason to connect all the dots within the 
kernel and actually *discover* nd use the very, very likely 
performance preference of the hardware in question.

Like a good resource management system (==kernel) should do.

We can do that with a 99% confidence factor or so - maybe better 
- and leave all the weird cases that the kernel cannot (or 
should not) know about to 'user space policy' knobs.

Thanks,

	Ingo