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From:   Thomas Gleixner <tglx@linutronix.de>
To:     boris.ostrovsky@oracle.com, LKML <linux-kernel@vger.kernel.org>
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Subject: Re: [patch 27/30] xen/events: Only force affinity mask for percpu interrupts
In-Reply-To: <7f7af60f-567f-cdef-f8db-8062a44758ce@oracle.com>
References: <20201210192536.118432146@linutronix.de> <20201210194045.250321315@linutronix.de> <7f7af60f-567f-cdef-f8db-8062a44758ce@oracle.com>
Date:   Fri, 11 Dec 2020 01:06:59 +0100
Message-ID: <87ft4di4t8.fsf@nanos.tec.linutronix.de>
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On Thu, Dec 10 2020 at 18:20, boris ostrovsky wrote:
> 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 stor=
ed
>> 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 w=
ill
>> be updated.=20
>
> If that's the case then I wonder whether we need this call at all and
> instead bind at startup time.

I was wondering about that, but my knowledge about the Xen internal
requirements is pretty limited. The current set at least survived basic
testing by J=C3=BCrgen.

Thanks,

        tglx