linux-kernel - Re: [PATCH V5] xen: privcmd: Add support for irqfd

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Message-ID: <54463c4e-53a3-42ef-9d9f-541f89e8c9ef@suse.com>
Date:   Tue, 22 Aug 2023 12:13:20 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Alex Bennée <alex.bennee@...aro.org>,
        stratos-dev@...lists.linaro.org,
        Erik Schilling <erik.schilling@...aro.org>,
        Manos Pitsidianakis <manos.pitsidianakis@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5] xen: privcmd: Add support for irqfd

On 22.08.23 11:45, Viresh Kumar wrote:
> Xen provides support for injecting interrupts to the guests via the
> HYPERVISOR_dm_op() hypercall. The same is used by the Virtio based
> device backend implementations, in an inefficient manner currently.
> 
> Generally, the Virtio backends are implemented to work with the Eventfd
> based mechanism. In order to make such backends work with Xen, another
> software layer needs to poll the Eventfds and raise an interrupt to the
> guest using the Xen based mechanism. This results in an extra context
> switch.
> 
> This is not a new problem in Linux though. It is present with other
> hypervisors like KVM, etc. as well. The generic solution implemented in
> the kernel for them is to provide an IOCTL call to pass the interrupt
> details and eventfd, which lets the kernel take care of polling the
> eventfd and raising of the interrupt, instead of handling this in user
> space (which involves an extra context switch).
> 
> This patch adds support to inject a specific interrupt to guest using
> the eventfd mechanism, by preventing the extra context switch.
> 
> Inspired by existing implementations for KVM, etc..
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen


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