linux-kernel - Re: [KVM PATCH 1/2] KVM: Directly inject interrupts via irqfd

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Date:	Thu, 22 Oct 2009 17:19:48 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gregory Haskins <gregory.haskins@...il.com>
CC:	Gleb Natapov <gleb@...hat.com>,
	Gregory Haskins <ghaskins@...ell.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	alacrityvm-devel@...ts.sourceforge.net
Subject: Re: [KVM PATCH 1/2] KVM: Directly inject interrupts via irqfd

On 10/22/2009 05:14 PM, Gregory Haskins wrote:
> Yeah, I was thinking about that after I initially responded to Gleb.
>
> I am thinking something along these lines:
>
> Provide a function that lets you query a GSI for whether it supports
> LOCKLESS or not.  Then we can either do one of two things:
>
> 1) Check for the LOCKLESS attribute at irqfd registration, fail if not
> present
>    

This is the most practical path and leads to the smallest code.  However 
it has the deficiency of exposing internal implementation details to 
userspace.  In theory userspace could use msi and edge-triggered 
pic/ioapic interrupts equally well, it shouldn't have to know that we 
didn't bother to lockfree ioapic/pic.

> 2) Cache the LOCKLESS attribute in the irqfd structure, and either go
> direct or defer to a workqueue depending on the flag.
>    

While this leads to larger code, it is more consistent.

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

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