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

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Date:	Thu, 27 Sep 2012 12:20:57 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.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 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. The user-specified
affinity still has the cpu that 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.

hope this clears it!

thanks.

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