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Subject: Re: [patch 27/30] xen/events: Only force affinity mask for percpu
 interrupts
To:     Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
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References: <20201210192536.118432146@linutronix.de>
 <20201210194045.250321315@linutronix.de>
From:   boris.ostrovsky@oracle.com
Organization: Oracle Corporation
Message-ID: <7f7af60f-567f-cdef-f8db-8062a44758ce@oracle.com>
Date:   Thu, 10 Dec 2020 18:20:46 -0500
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On 12/10/20 2:26 PM, Thomas Gleixner wrote:
> All event channel setups bind the interrupt on CPU0 or the target CPU for
> percpu interrupts and overwrite the affinity mask with the corresponding
> cpumask. That does not make sense.
>
> The XEN implementation of irqchip::irq_set_affinity() already picks a
> single target CPU out of the affinity mask and the actual target is stored
> in the effective CPU mask, so destroying the user chosen affinity mask
> which might contain more than one CPU is wrong.
>
> Change the implementation so that the channel is bound to CPU0 at the XEN
> level and leave the affinity mask alone. At startup of the interrupt
> affinity will be assigned out of the affinity mask and the XEN binding will
> be updated. 


If that's the case then I wonder whether we need this call at all and instead bind at startup time.


-boris


> Only keep the enforcement for real percpu interrupts.