Message-ID: <551B9514.80701@linux.vnet.ibm.com>
Date: Wed, 01 Apr 2015 12:19:56 +0530
From: Preeti U Murthy <preeti@linux.vnet.ibm.com>
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To: Jason Low <jason.low2@hp.com>
CC: peterz@infradead.org, mingo@kernel.org,
        Daniel Lezcano <daniel.lezcano@linaro.org>, riel@redhat.com,
        vincent.guittot@linaro.org, srikar@linux.vnet.ibm.com, pjt@google.com,
        benh@kernel.crashing.org, efault@gmx.de, linux-kernel@vger.kernel.org,
        iamjoonsoo.kim@lge.com, svaidy@linux.vnet.ibm.com,
        tim.c.chen@linux.intel.com, morten.rasmussen@arm.com
Subject: Re: sched: Improve load balancing in the presence of idle CPUs
References: <1427741729.5694.24.camel@j-VirtualBox> <551A5CCE.70008@linux.vnet.ibm.com> <1427828056.2492.24.camel@j-VirtualBox>
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On 04/01/2015 12:24 AM, Jason Low wrote:
> On Tue, 2015-03-31 at 14:07 +0530, Preeti U Murthy wrote:
>> Hi Jason,
>>
>> On 03/31/2015 12:25 AM, Jason Low wrote:
>>> Hi Preeti,
>>>
>>> I noticed that another commit 4a725627f21d converted the check in
>>> nohz_kick_needed() from idle_cpu() to rq->idle_balance, causing a
>>> potentially outdated value to be used if this cpu is able to pull tasks
>>> using rebalance_domains(), and nohz_kick_needed() directly returning
>>> false.
>>
>> I see that rebalance_domains() will be run at the end of the scheduler
>> tick interrupt handling. trigger_load_balance() only sets the softirq,
>> it does not call rebalance_domains() immediately. So the call graph
>> would be:
> 
> Oh right, since that only sets the softirq, this wouldn't be the issue,
> though we would need these changes if we were to incorporate any sort of
> nohz_kick_needed() logic into the nohz_idle_balance() code path correct?

I am sorry I don't quite get this. Can you please elaborate?

Regards
Preeti U Murthy
> 

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