linux-kernel - Re: [patch 32/32] genirq/msi: Convert storage to xarray

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Date:   Sat, 27 Nov 2021 13:33:24 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zygnier <maz@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Megha Dey <megha.dey@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, linux-pci@...r.kernel.org,
        linux-s390@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <allenbh@...il.com>, linux-ntb@...glegroups.com
Subject: Re: [patch 32/32] genirq/msi: Convert storage to xarray

On Sat, Nov 27, 2021 at 02:23:17AM +0100, Thomas Gleixner wrote:
> The current linked list storage for MSI descriptors is suboptimal in
> several ways:
> 
>   1) Looking up a MSI desciptor requires a O(n) list walk in the worst case
> 
>   2) The upcoming support of runtime expansion of MSI-X vectors would need
>      to do a full list walk to figure out whether a particular index is
>      already associated.
> 
>   3) Runtime expansion of sparse allocations is even more complex as the
>      current implementation assumes an ordered list (increasing MSI index).
> 
> Use an xarray which solves all of the above problems nicely.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/msi.h |   19 ++---
>  kernel/irq/msi.c    |  188 ++++++++++++++++++++++------------------------------
>  2 files changed, 90 insertions(+), 117 deletions(-)

Much simpler code too, nice!

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>