linux-kernel - Re: [PATCH RESEND] x86/fixup_irq: Clean the offlining CPU from the irq affinity mask

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Date:	Fri, 28 Sep 2012 02:03:24 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
CC:	Chuansheng Liu <chuansheng.liu@...el.com>, tglx@...utronix.de,
	mingo@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org,
	yanmin_zhang@...ux.intel.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>
Subject: Re: [PATCH RESEND] x86/fixup_irq: Clean the offlining CPU from the
 irq affinity mask

On 09/28/2012 12:50 AM, Suresh Siddha wrote:
> On Fri, 2012-09-28 at 00:12 +0530, Srivatsa S. Bhat wrote:
>> On 09/27/2012 04:16 AM, Suresh Siddha wrote:
>>>
>>> No. irq_set_affinity()
>>>
>>
>> Um? That takes the updated/changed affinity and sets data->affinity to
>> that value no? You mentioned that probably the intention of the original
>> code was to preserve the user-set affinity mask, but still change the
>> underlying interrupt routing. Sorry, but I still didn't quite understand
>> what is that part of the code that achieves that.
> 
> For the HW routing to be changed we AND it with cpu_online_map and use
> that for programming the interrupt entries etc.

Ah, now I see.. you were referring to the __assign_irq_vector() code, whereas
I was looking only at fixup_irqs() and was trying to find the code that did
what you said.. that's what got me confused earlier :-)

> The user-specified
> affinity still has the cpu that is offlined.
> 

Right, so data->affinity is untouched, whereas cfg->domain is updated when
the CPU is offlined..

> And when the cpu comes online and if it is part of the user-specified
> affinity, then the HW routing can be again modified to include the new
> cpu.
> 

Right, got it.

> hope this clears it!
>

Yep, thanks a lot!

Regards,
Srivatsa S. Bhat

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