linux-kernel - Re: [PATCH v8 0/6] kvm: level irqfd support

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Message-ID: <502D2099.7050800@redhat.com>
Date:	Thu, 16 Aug 2012 19:32:25 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
CC:	mst@...hat.com, gleb@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 0/6] kvm: level irqfd support

On 08/11/2012 01:37 AM, Alex Williamson wrote:
> v8:
> 
> Trying a new approach.  Nobody seems to like the internal IRQ
> source ID object and the interactions it implies between irqfd
> and eoifd, so let's get rid of it.  Instead, simply expose
> IRQ source IDs to userspace.  This lets the user be in charge
> of freeing them or hanging onto a source ID for later use.  They
> can also detach and re-attach components at will.  It also opens
> up the possibility that userspace might want to use each IRQ
> source ID for more than one GSI (and avoids the kernel needing
> to manage that).  Per suggestions, EOIFD is now IRQ_ACKFD.
> 
> I really wanted to add a de-assert-only option to irqfd so the
> irq_ackfd could be fed directly into an irqfd, but I'm dependent
> on the ordering of de-assert _then_ signal an eventfd.  Keeping
> that ordering doesn't seem to be possible, especially since irqfd
> uses a workqueue, if I attempt to make that connection.  Thanks,

I can't say I'm happy with exposing irq source IDs.  It's true that they
correspond to a physical entity so they can't be said to be an
implementation detail, but adding more ABIs has a cost and I can't say
that I see another user for this.

Can you provide a link to the combined irqfd+ackfd implementation?  I'm
inclined now to go for the simplest solution possible.

-- 
error compiling committee.c: too many arguments to function
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