linux-kernel - Re: [PATCH v2] PCI: Equalize hotplug memory for non/occupied slots

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Date:   Fri, 31 Aug 2018 16:51:35 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Jon Derrick <jonathan.derrick@...el.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Keith Busch <keith.busch@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sinan Kaya <okaya@...nel.org>, Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [PATCH v2] PCI: Equalize hotplug memory for non/occupied slots

On Thu, Aug 30, 2018 at 04:12:00PM -0600, Jon Derrick wrote:
> Currently, a hotplug bridge will be given hpmemsize additional memory if
> available, in order to satisfy any future hotplug allocation
> requirements.
> 
> These calculations don't consider the current memory size of the hotplug
> bridge/slot, so hotplug bridges/slots which have downstream devices will
> get their current allocation in addition to the hpmemsize value.
> 
> This makes for possibly undesirable results with a mix of unoccupied and
> occupied slots (ex, with hpmemsize=2M):
> 
> 02:03.0 PCI bridge: <-- Occupied
> 	Memory behind bridge: d6200000-d64fffff [size=3M]
> 02:04.0 PCI bridge: <-- Unoccupied
> 	Memory behind bridge: d6500000-d66fffff [size=2M]
> 
> This change considers the current allocation size when using the
> hpmemsize parameter to make the reservations predictable for the mix of
> unoccupied and occupied slots:
> 
> 02:03.0 PCI bridge: <-- Occupied
> 	Memory behind bridge: d6200000-d63fffff [size=2M]
> 02:04.0 PCI bridge: <-- Unoccupied
> 	Memory behind bridge: d6400000-d65fffff [size=2M]
> 
> The calculation for IO (hpiosize) should be similar, but platform
> firmwares I've encountered (including QEMU) provide strict allocations
> for IO and would not provide free IO resources for hotplug buses
> in order to prove this calculation.
> 
> Signed-off-by: Jon Derrick <jonathan.derrick@...el.com>

Reviewed-by: Mika Westerberg <mika.westerberg@...ux.intel.com>