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

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Date:	Tue, 10 Jan 2012 00:58:56 -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

> Note, this has the hard-coded assumption you only have 2 threads per
> core, which while true for intel, isn't true in general. I think you
> meant to write *= group->group_weight or somesuch.
> 
> Also, you forgot to limit this to the SD_SHARE_CPUPOWER domain, you're
> now doubling the capacity for all domains.
> 
> Furthermore, have a look at the SD_PREFER_SIBLING logic and make sure
> you're not fighting that.
> 
Thanks Peter! Here is the patch. 

-Youquan

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a4d2b7a..4ada3e7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -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 && !(sd->flags & SD_SHARE_CPUPOWER))
+               sgs->group_capacity = group->group_weight;
+
        sgs->group_weight = group->group_weight;

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