linux-kernel - Re: [PATCH v3 0/3] genirq/vfio: Introduce update_irq

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Date:   Mon, 19 Aug 2019 14:51:50 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Ben Luo <luoben@...ux.alibaba.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org,
        tao.ma@...ux.alibaba.com, gerry@...ux.alibaba.com,
        nanhai.zou@...ux.alibaba.com, linyunsheng@...wei.com
Subject: Re: [PATCH v3 0/3] genirq/vfio: Introduce update_irq_devid and
 optimize VFIO irq ops

On Thu, 15 Aug 2019 21:02:58 +0800
Ben Luo <luoben@...ux.alibaba.com> wrote:

> Currently, VFIO takes a lot of free-then-request-irq actions whenever
> a VM (with device passthru via VFIO) sets irq affinity or mask/unmask
> irq. Those actions only change the cookie data of irqaction or even
> change nothing. The free-then-request-irq not only adds more latency,
> but also increases the risk of losing interrupt, which may lead to a
> VM hung forever in waiting for IO completion

What guest environment is generating this?  Typically I don't see that
Windows or Linux guests bounce the interrupt configuration much.
Thanks,

Alex

> 
> This patchset solved the issue by:
> Patch 2 introduces update_irq_devid to only update dev_id of irqaction
> Patch 3 make use of update_irq_devid and optimize irq operations in VFIO
> 
> changes from v2:
>  - reformat to avoid quoted string split across lines and etc.
> 
> changes from v1:
>  - add Patch 1 to enhance error recovery etc. in free irq per tglx's comments
>  - enhance error recovery code and debugging info in update_irq_devid
>  - use __must_check in external referencing of update_irq_devid
>  - use EXPORT_SYMBOL_GPL for update_irq_devid
>  - reformat code of patch 3 for better readability
> 
> Ben Luo (3):
>   genirq: enhance error recovery code in free irq
>   genirq: introduce update_irq_devid()
>   vfio_pci: make use of update_irq_devid and optimize irq ops
> 
>  drivers/vfio/pci/vfio_pci_intrs.c | 101 +++++++++++++++++++++-------------
>  include/linux/interrupt.h         |   3 ++
>  kernel/irq/manage.c               | 110 +++++++++++++++++++++++++++++++++-----
>  3 files changed, 164 insertions(+), 50 deletions(-)
>