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Subject: Re: [patch 27/30] xen/events: Only force affinity mask for percpu
 interrupts
References: <20201210192536.118432146@linutronix.de>
 <20201210194045.250321315@linutronix.de>
From: boris.ostrovsky@oracle.com
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Date: Thu, 10 Dec 2020 18:20:46 -0500
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To: Thomas Gleixner <tglx@linutronix.de>, LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Marc Zyngier <maz@kernel.org>, Juergen Gross <jgross@suse.com>, Stefano Stabellini <sstabellini@kernel.org>, xen-devel@lists.xenproject.org, "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>, Helge Deller <deller@gmx.de>, afzal mohammed <afzal.mohd.ma@gmail.com>, linux-parisc@vger.kernel.org, Russell King <linux@armlinux.org.uk>, linux-arm-kernel@lists.infradead.org, Mark Rutland <mark.rutland@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Christian Borntraeger <borntraeger@de.ibm.com>, Heiko Carstens <hca@linux.ibm.com>, linux-s390@vger.kernel.org, Jani Nikula <jani.nikula@linux.intel.com>, Joonas Lahtinen <joonas.lahtinen@linux.intel.com>, Rodrigo Vivi <rodrigo.vivi@intel.com>, David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>, Pankaj Bharadiya <pankaj.laxminarayan.bharadiya@intel.com>, Chris Wilson <chris@chris-wilson.co.uk>, Wambui Karuga <wambui.karugax@gmail.com>, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>, Linus Walleij <linus.walleij@linaro.org>, linux-gpio@vger.kernel.org, Lee Jones <lee.jones@linaro.org>, Jon Mason <jdmason@kudzu.us>, Dave Jiang <dave.jiang@intel.com>, Allen Hubbe <allenbh@gmail.com>, linux-ntb@googlegroups.com, Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>, Rob Herring <robh@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>, Michal Simek <michal.simek@xilinx.com>, linux-pci@vger.kernel.org, Karthikeyan Mitran <m.karthikeyan@mobiveil.co.in>, Hou Zhiqiang <Zhiqiang.Hou@nxp.com>, Tariq Toukan <tariqt@nvidia.com>, "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, Saeed Mahameed <saeedm@nvidia.com>, Leon Romanovsky <leon@kernel.org>


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.