linux-kernel - Re: [kvm-devel] [PATCH 10/13] KVM: Wire up hypercall handlers to a central arch-independent location

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Message-ID: <45DD9A9D.4060500@qumranet.com>
Date:	Thu, 22 Feb 2007 15:29:01 +0200
From:	Avi Kivity <avi@...ranet.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Dor Laor <dor.laor@...ranet.com>, Pavel Machek <pavel@....cz>,
	kvm-devel@...ts.sourceforge.net, akpm@...l.org,
	linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH 10/13] KVM: Wire up hypercall handlers to
 a	central arch-independent location

Arjan van de Ven wrote:
>> Somthing else that came up in a conversation with Dor: the need for a 
>> clean way to raise a guest interrupt.  The guest may be sleeping in 
>> userspace, scheduled out, or running on another cpu (and requiring an 
>> ipi to get it out of guest mode).
>>     
>
> yeah it'd be nice if I could just call a function for it rather than
> poking into kvm internals ;)
>
>   

Sure.  Please report all inconveniences (they're really bugs) so we can 
fix them.

Poking at kvm internals means you waste your time learning them, and 
later we can't change them.


>> Right now I'm thinking about using the signal machinery since it appears 
>> to do exactly the right thing.
>>     
>
> signals are *expensive* though.
>
>   

I think the expensive part of signals is userspace delivery.  If they 
are always blocked in userspace, they become just another IPC channel.

I plan to add a signal mask to KVM_RUN a la pselect() so that userspace 
can dequeue signals instead of using a signal handler.


> If you design an interrupt interface, it'd rock if you could make it
> such that it is "raise <this> interrupt within <x> miliseconds from
> now", rather than making it mostly synchronous. That way irq mitigation
> becomes part of the interface rather than having to duplicate it all
> over the virtual drivers...
>   

Can't it be done by a helper function using a timer and a signal (or 
whatever mechanism we use to wake up vcpus)?

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

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