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Re: [RFC PATCH 02/10] xen: pci: add pci_seg->alldevs_lock
- To: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 28 Feb 2023 17:32:05 +0100
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- Cc: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, Paul Durrant <paul@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 28 Feb 2023 16:32:24 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 31.08.2022 16:10, Volodymyr Babchuk wrote:
> This lock protects alldevs_list of struct pci_seg. As this, it should
> be used when we are adding, removing on enumerating PCI devices
> assigned to a PCI segment.
>
> Radix tree that stores PCI segment has own locking mechanism, also
> pci_seg structures are only allocated and newer freed, so we need no
> additional locking to access pci_seg structures. But we need a lock
> that protects alldevs_list field.
>
> This enables more granular locking instead of one huge pcidevs_lock
> that locks entire PCI subsystem. Please note that pcidevs_lock() is
> still used, we are going to remove it in subsequent patches.
Just a thought: To limit the scope of the steps taken, would it be a
possibility (and useful) to move from the global to the per-segment
lock, extending what this per-segment lock is actually protecting?
And only then take further steps, as already done in later parts of
this series?
Jan
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