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Subject: Re: [patch 27/30] xen/events: Only force affinity mask for percpu
 interrupts
To:     boris.ostrovsky@oracle.com, Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Marc Zyngier <maz@kernel.org>,
        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>
References: <20201210192536.118432146@linutronix.de>
 <20201210194045.250321315@linutronix.de>
 <7f7af60f-567f-cdef-f8db-8062a44758ce@oracle.com>
From:   =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
Message-ID: <2164a0ce-0e0d-c7dc-ac97-87c8f384ad82@suse.com>
Date:   Fri, 11 Dec 2020 13:10:43 +0100
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From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>
To: boris.ostrovsky@oracle.com, Thomas Gleixner <tglx@linutronix.de>,
 LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Marc Zyngier <maz@kernel.org>,
 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>
Message-ID: <2164a0ce-0e0d-c7dc-ac97-87c8f384ad82@suse.com>
Subject: Re: [patch 27/30] xen/events: Only force affinity mask for percpu
 interrupts
References: <20201210192536.118432146@linutronix.de>
 <20201210194045.250321315@linutronix.de>
 <7f7af60f-567f-cdef-f8db-8062a44758ce@oracle.com>
In-Reply-To: <7f7af60f-567f-cdef-f8db-8062a44758ce@oracle.com>

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On 11.12.20 00:20, boris.ostrovsky@oracle.com wrote:
>=20
> 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 correspondi=
ng
>> 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 st=
ored
>> 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.
>=20
>=20
> If that's the case then I wonder whether we need this call at all and i=
nstead bind at startup time.

After some discussion with Thomas on IRC and xen-devel archaeology the
result is: this will be needed especially for systems running on a
single vcpu (e.g. small guests), as the .irq_set_affinity() callback
won't be called in this case when starting the irq.


Juergen

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