linux-kernel - Re: [PATCH 0/4] time: dynamic irq affinity

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Date:	Mon, 11 Mar 2013 10:28:29 +0100
From:	Rickard Andersson <rickard.andersson@...ricsson.com>
To:	Santosh Shilimkar <santosh.shilimkar@...com>
Cc:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"john.stultz@...aro.org" <john.stultz@...aro.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
	"jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	Linus WALLEIJ <linus.walleij@...ricsson.com>
Subject: Re: [PATCH 0/4] time: dynamic irq affinity

On 03/11/2013 10:12 AM, Santosh Shilimkar wrote:
> On Monday 11 March 2013 02:10 PM, Daniel Lezcano wrote:
>> On 03/11/2013 04:24 AM, Santosh Shilimkar wrote:
>>> On Sunday 10 March 2013 11:52 PM, Daniel Lezcano wrote:
>> [ ... ]
>>
>>>> I don't think it is the case for all the ARM platforms, at least we
>>>> tested it on vexpress TC2 and u8500, and the number of IPI were reduced
>>>> very significantly increasing the idle time for cpu0. TC2 will need
>>>> another optimization on another area for the idle wake up to gain real
>>>> improvements.
>>>>
>>> You are missing my point. TC2 can be an exception since the SGI can wakeup
>>> CPUs even from low power states where local timer's are stalled. Is that
>>> the case with U8500 ?
>> Well, the cpuidle driver is not going into a deep idle state to check
>> this out.
>>
>> AFAICT this board has a specific firmware with the PRCMU (a device
>> managing the power on the board) and it replaces the GIC when going to
>> deep idle state, especially by reconnecting the GIC to the A9 cores
>> automatically when an interrupt occurs.
>>
> But most likely it will be limited to peripheral interrupts. SGI's
> are per-cpu irq's so you need to check that part.
>
In the U8500 case, when the first CPU is woken up it will work ok for 
that CPU to send an IPI to the other CPU.

BR
Rickard
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