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Message-ID: <4AE07B2F.2040508@gmail.com>
Date: Thu, 22 Oct 2009 11:33:03 -0400
From: Gregory Haskins <gregory.haskins@gmail.com>
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To: Avi Kivity <avi@redhat.com>
CC: Gleb Natapov <gleb@redhat.com>, Gregory Haskins <ghaskins@novell.com>,
       kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
       alacrityvm-devel@lists.sourceforge.net
Subject: Re: [KVM PATCH 1/2] KVM: Directly inject interrupts via irqfd
References: <20091021143042.14955.22470.stgit@dev.haskins.net> <20091021143453.14955.80578.stgit@dev.haskins.net> <20091021152621.GR29477@redhat.com> <4ADF2A1B.3010205@gmail.com> <20091021153640.GS29477@redhat.com> <4ADF2BDD.40706@gmail.com> <4AE07541.8060903@redhat.com> <4AE076E0.7030100@gmail.com> <4AE07814.6020906@redhat.com>
In-Reply-To: <4AE07814.6020906@redhat.com>
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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
>>   =20
>=20
> This is the most practical path and leads to the smallest code.  Howeve=
r
> 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.
>=20
>> 2) Cache the LOCKLESS attribute in the irqfd structure, and either go
>> direct or defer to a workqueue depending on the flag.
>>   =20
>=20
> While this leads to larger code, it is more consistent.
>=20

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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