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

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Message-ID: <4AE07B2F.2040508@gmail.com>
Date:	Thu, 22 Oct 2009 11:33:03 -0400
From:	Gregory Haskins <gregory.haskins@...il.com>
To:	Avi Kivity <avi@...hat.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

Avi Kivity wrote:
> 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.
> 

Yeah, I think you are right.  Consider these two patches retracted, and
I will rewrite it with this concept in place.

Kind Regards,
-Greg


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