Subject: Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods
To: Frederic Weisbecker <fweisbec@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Christoph Lameter <cl@linux.com>
Cc: Andi Kleen <ak@linux.intel.com>, Aubrey Li <aubrey.li@intel.com>,
        tglx@linutronix.de, len.brown@intel.com, rjw@rjwysocki.net,
        tim.c.chen@linux.intel.com, arjan@linux.intel.com,
        paulmck@linux.vnet.ibm.com, yang.zhang.wz@gmail.com, x86@kernel.org,
        linux-kernel@vger.kernel.org
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From: "Li, Aubrey" <aubrey.li@linux.intel.com>
Message-ID: <46cd0758-3bf9-a907-4b8d-5c7338934fc8@linux.intel.com>
Date: Wed, 12 Jul 2017 10:35:33 +0800
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On 2017/7/12 0:09, Frederic Weisbecker wrote:
> On Tue, Jul 11, 2017 at 11:41:57AM +0200, Peter Zijlstra wrote:
>>
>>> - totally from arch_cpu_idle_enter entry to arch_cpu_idle_exit return costs
>>>   9122ns - 15318ns.
>>>   --In this period, rcu_idle_enter costs 1985ns - 2262ns, rcu_idle_exit costs
>>>     1813ns - 3507ns
>>
>> Is that the POPF being painful? or something else?
> 
> Probably that and the atomic_add_return().
> We thought RCU idle cost is high, but it seems not. But it still has few microseconds
can be saved if we can remove them from fast idle path.

Thanks,
-Aubrey