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From: "Derrick, Jonathan" <jonathan.derrick@intel.com>
To: "kbusch@kernel.org" <kbusch@kernel.org>
Cc: "lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"helgaas@kernel.org" <helgaas@kernel.org>
Subject: Re: [PATCH 3/3] PCI: vmd: Use managed irq affinities
Date: Wed, 6 Nov 2019 20:14:41 +0000	[thread overview]
Message-ID: <0a4a4151b56567f3c8ca71a29a2e39add6e3bf77.camel@intel.com> (raw)
In-Reply-To: <20191106181032.GD29853@redsun51.ssa.fujisawa.hgst.com>

On Thu, 2019-11-07 at 03:10 +0900, Keith Busch wrote:
> On Wed, Nov 06, 2019 at 04:40:08AM -0700, Jon Derrick wrote:
> > Using managed IRQ affinities sets up the VMD affinities identically to
> > the child devices when those devices vector counts are limited by VMD.
> > This promotes better affinity handling as interrupts won't necessarily
> > need to pass context between non-local CPUs. One pre-vector is reserved
> > for the slow interrupt and not considered in the affinity algorithm.
> 
> This only works if all devices have exactly the same number of interrupts
> as the parent VMD host bridge. If a child device has less, the device
> will stop working if you offline a cpu: the child device may have a
> resource affined to other online cpus, but the VMD device affinity is to
> that single offline cpu.

Yes that problem exists today and this set limits the exposure as it's
a rare case where you have a child NVMe device with fewer than 32
vectors.

  reply	other threads:[~2019-11-06 20:14 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-06 11:40 [PATCH 0/3] PCI: vmd: Reducing tail latency by affining to the storage stack Jon Derrick
2019-11-06 11:40 ` [PATCH 1/3] PCI: vmd: Reduce VMD vectors using NVMe calculation Jon Derrick
2019-11-06 18:02   ` Keith Busch
2019-11-06 19:51     ` Derrick, Jonathan
2019-11-06 11:40 ` [PATCH 2/3] PCI: vmd: Align IRQ lists with child device vectors Jon Derrick
2019-11-06 18:06   ` Keith Busch
2019-11-06 20:14     ` Derrick, Jonathan
2019-11-06 11:40 ` [PATCH 3/3] PCI: vmd: Use managed irq affinities Jon Derrick
2019-11-06 18:10   ` Keith Busch
2019-11-06 20:14     ` Derrick, Jonathan [this message]
2019-11-06 20:27       ` Keith Busch
2019-11-06 20:33         ` Derrick, Jonathan
2019-11-18 10:49           ` Lorenzo Pieralisi
2019-11-18 16:43             ` Derrick, Jonathan
2019-11-07  9:39 ` [PATCH 0/3] PCI: vmd: Reducing tail latency by affining to the storage stack Christoph Hellwig
2019-11-07 14:12   ` Derrick, Jonathan
2019-11-07 15:37     ` hch
2019-11-07 15:40       ` Derrick, Jonathan
2019-11-07 15:42         ` hch
2019-11-07 15:47           ` Derrick, Jonathan
2019-11-11 17:03             ` hch
2022-12-23  2:33 ` Kai-Heng Feng

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