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

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Message-ID: <20120111173744.GA27967@linux-youquan.bj.intel.com>
Date:	Wed, 11 Jan 2012 12:37:44 -0500
From:	Youquan Song <youquan.song@...el.com>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Youquan Song <youquan.song@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, akpm@...ux-foundation.org, stable@...r.kernel.org,
	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

> I had tested sched_mc_powersavings=2 on dual socket quad core HT
> nehalem.  It worked as expected.  Let me check the
> sched_mc_powersavings=1 case.  I will not be surprised if it is
> broken.
> 
 
In my opinion. When CPU cores > 8, sched_mc will have issue of course.
What's more, when CPU cores increase it will be abviously if following
current CPU power capability calcaluation logic.

If CPU has 8 cores and if HT enabled, its power capability > 9 cores. 
Current logic, HT enable core power capability = 1178,  1178 * 8
/ 1024 > 9.2. So scheduler will try to schedule >8 threads to meet its
power capability before use other socket if sched_mc used.

So it will be better, like this: Of course, It is only sample code
and I do not try it yet.

For MC:
+       if (sched_mc_power_savings)
+               sgs->group_capacity = group->group_weight/2;

For SMT:
+       if (sched_smt_power_savings && !(sd->flags & SD_SHARE_CPUPOWER))
+               sgs->group_capacity = group->group_weight;


Thanks
-Youquan
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