Subject: Re: [RFC PATCH v2 0/2] sched: Nominate a power-efficient ILB
From: Suresh Siddha <suresh.b.siddha@intel.com>
Reply-To: suresh.b.siddha@intel.com
To: Gautham R Shenoy <ego@in.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       Balbir Singh <balbir@in.ibm.com>, Andi Kleen <andi@firstfloor.org>,
       Randy Dunlap <randy.dunlap@oracle.com>
In-Reply-To: <20090414045356.7645.33369.stgit@sofia.in.ibm.com>
References: <20090414045356.7645.33369.stgit@sofia.in.ibm.com>
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Organization: Intel Corp
Date: Tue, 21 Apr 2009 18:05:22 -0700
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On Mon, 2009-04-13 at 21:55 -0700, Gautham R Shenoy wrote:
> Now, the other power-savings settings such as the sched_mc/smt_power_savings
> and the power-aware IRQ balancer try to balance tasks/IRQs by taking
> the system topology into consideration, with the intention of keeping
> as many "power-domains" (cores/packages) in the low-power state.
> 
> The current idle-load-balancer nomination does not necessarily align towards
> this policy. For eg, we could be having tasks and interrupts largely running
> on the first package with the intention of keeping the second package idle.
> Hence, CPU 0 may be busy. The first_cpu in the nohz.cpu_mask happens to be CPU1,
> which in-turn becomes nominated as the idle-load balancer. CPU1 being from
> the 2nd package, would in turn prevent the 2nd package from going into a
> deeper sleep state.
> 
> Instead the role of the idle-load balancer could have been assumed by an
> idle CPU from the first package, thereby helping the second package go
> completely idle.

Can we also do this by default? i.e., even when no power-savings policy
is selected.

I don't see anything wrong by enabling this logic for all the cases.

thanks,
suresh

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