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Subject: Re: [PATCH RESEND] x86/fixup_irq: Clean the offlining CPU from the
 irq affinity mask
From: Suresh Siddha <suresh.b.siddha@intel.com>
Reply-To: Suresh Siddha <suresh.b.siddha@intel.com>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Chuansheng Liu <chuansheng.liu@intel.com>, tglx@linutronix.de,
        mingo@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org,
        yanmin_zhang@linux.intel.com,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "rusty@rustcorp.com.au" <rusty@rustcorp.com.au>
Date: Thu, 27 Sep 2012 12:20:57 -0700
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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.