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Message-ID: <4AE5A336.4010801@gmail.com>
Date: Mon, 26 Oct 2009 09:25:10 -0400
From: Gregory Haskins <gregory.haskins@gmail.com>
User-Agent: Thunderbird 2.0.0.23 (Macintosh/20090812)
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To: Avi Kivity <avi@redhat.com>
CC: Gregory Haskins <ghaskins@novell.com>, linux-kernel@vger.kernel.org,
       kvm@vger.kernel.org, alacrityvm-devel@lists.sourceforge.net
Subject: Re: [Alacrityvm-devel] [KVM PATCH v2 1/2] KVM: export lockless GSI
 attribute
References: <20091023023512.3891.65889.stgit@dev.haskins.net>	<20091023023845.3891.36857.stgit@dev.haskins.net> <4AE460F4.2090905@redhat.com>
In-Reply-To: <4AE460F4.2090905@redhat.com>
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Avi Kivity wrote:
> On 10/23/2009 04:38 AM, Gregory Haskins wrote:
>> Certain GSI's support lockless injecton, but we have no way to detect
>> which ones at the GSI level.  Knowledge of this attribute will be
>> useful later in the series so that we can optimize irqfd injection
>> paths for cases where we know the code will not sleep.  Therefore,
>> we provide an API to query a specific GSI.
>>
>>   =20
>=20
> Instead of a lockless attribute, how about a ->set_atomic() method.  Fo=
r=20
> msi this can be the same as ->set(), for non-msi it can be a function=20
> that schedules the work (which will eventually call ->set()).
>=20
> The benefit is that we make a decision only once, when preparing the=20
> routing entry, and install that decision in the routing entry instead o=
f=20
> making it again and again later.

Yeah, I like this idea.  I think we can also get rid of the custom
workqueue if we do this as well, TBD.

>=20
>> +int kvm_irq_check_lockless(struct kvm *kvm, u32 irq)
>>   =20
>=20
> bool kvm_irq_check_lockless(...)

We lose the ability to detect failure (such as ENOENT) if we do this,
but its moot if we move to the ->set_atomic() model, since this
attribute is no longer necessary and this patch can be dropped.

Kind Regards,
-Greg


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