linux-kernel - Re: [PATCH] x86,sched: Fix sched_smt_power

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Date:	Mon, 9 Jan 2012 19:14:45 -0500
From:	Youquan Song <youquan.song@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Youquan Song <youquan.song@...el.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, akpm@...ux-foundation.org, stable@...r.kernel.org,
	suresh.b.siddha@...el.com, arjan@...ux.intel.com,
	len.brown@...el.com, anhua.xu@...el.com, chaohong.guo@...el.com,
	Youquan Song <youquan.song@...ux.intel.com>
Subject: Re: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken

> Yes it is.. also that knob should die! Like i've been saying for way too
> long. I'm >< close to committing a patch removing all the power_saving
> magic from the scheduler.
Sorry. I do not notice it.
But currently in many real tests, the knob prove to save power in semi-idle system.
They are useful in many user scenarios currently.

> That's the most convoluted way I've seen that stated in a while. What
> you're saying is that all threads (of a socket) should be used before
> spilling over to another socket.
Only touch half. 
Another half: in ideal, all threads in one core be used before spilling over to another
core.

> Hell no, that's completely the wrong thing to do. I think you want to
> frob at the group_capacity computation in update_sg_lb_stats.
> 

Yes. It also can do in the ways you said. 
I have following testing code before which is changed in update_sg_lb_stats, 
but there are more refresh code required for fix. 
Fine, I will base your suggestion to develop another patch soon.

Thanks
-Youquan

@@ -3923,6 +3923,10 @@ static inline void update_sg_lb_stats(struct
sched_domain *sd,
                                                SCHED_POWER_SCALE);
        if (!sgs->group_capacity)
                sgs->group_capacity = fix_small_capacity(sd, group);
+
+       if (sched_smt_power_savings)
+               sgs->group_capacity *= 2;
+
        sgs->group_weight = group->group_weight;

        if (sgs->group_capacity > sgs->sum_nr_running)

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