Re: [patch v5 04/15] sched: add sched balance policies in kernel

From: Alex Shi
Date: Wed Feb 20 2013 - 08:40:49 EST

On 02/20/2013 05:37 PM, Ingo Molnar wrote:
> * Alex Shi <alex.shi@xxxxxxxxx> wrote:
>> Current scheduler behavior is just consider for larger
>> performance of system. So it try to spread tasks on more cpu
>> sockets and cpu cores
>> To adding the consideration of power awareness, the patchset
>> adds 2 kinds of scheduler policy: powersaving and balance.
>> They will use runnable load util in scheduler balancing. The
>> current scheduling is taken as performance policy.
>> performance: the current scheduling behaviour, try to spread tasks
>> on more CPU sockets or cores. performance oriented.
>> powersaving: will pack tasks into few sched group until all LCPU in the
>> group is full, power oriented.
>> balance : will pack tasks into few sched group until group_capacity
>> numbers CPU is full, balance between performance and
>> powersaving.
> Hm, so in a previous review I suggested keeping two main
> policies: power-saving and performance, plus a third, default
> policy, which automatically switches between these two if/when
> the kernel has information about whether a system is on battery
> or on AC - and picking 'performance' when it has no information.

I will try to add a default policy according to your suggestion.
> Such an automatic policy would obviously be useful to users -
> and that is what makes such a feature really interesting and a
> step forward.
> I think Peter expressed similar views: we don't want many knobs
> and states, we want two major goals plus an (optional but
> default enabled) automatism.

I got the message. thanks for reclaim again.

Now there is just 2 types policy: performance and powersaving(with 2
degrees, powersaving and balance).

powersaving policy will try to assign one task to each LCPU, whichever
the LCPU is SMT thread or a core.
The balance policy is also a kind of powersaving policy, just a bit less
aggressive. It will try to assign tasks according group capacity, one
task to one capacity.
It was introduced just because SMT LCPU in intel arch. SMT thread is a
independent LCPU in software, but its cpu power(smt_gain 1178 / 2 = 589)
is smaller than a normal CPU(1024). So, the group capacity is just 1 for
a 2 SMT thread core. So, on policy, just one task assign to one core

> Is your 'balance' policy implementing that suggestion?
> If not, why not?
> Thanks,
> Ingo

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