linux-kernel - Re: [PATCH] KVM: Improve interrupt response

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Date:	Tue, 2 Jan 2007 12:12:56 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...ranet.com>
Cc:	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	akpm@...l.org
Subject: Re: [PATCH] KVM: Improve interrupt response


* Avi Kivity <avi@...ranet.com> wrote:

> From: Dor Laor <dor.laor@...ranet.com>
> 
> The current interrupt injection mechanism might delay an interrupt 
> under the following circumstances:
> 
>  - if injection fails because the guest is not interruptible (rflags.IF clear,
>    or after a 'mov ss' or 'sti' instruction).  Userspace can check rflags,
>    but the other cases or not testable under the current API.
>  - if injection fails because of a fault during delivery.  This probably
>    never happens under normal guests.
>  - if injection fails due to a physical interrupt causing a vmexit so that
>    it can be handled by the host.
> 
> in all cases the guest proceeds without processing the interrupt, 
> reducing the interactive feel and interrupt throughput of the guest.
> 
> This patch fixes the situation by allowing userspace to request an 
> exit when the 'interrupt window' opens, so that it can re-inject the 
> interrupt at the right time.  Guest interactivity is very visibly 
> improved.

Andrew, i'd argue for this to be included in v2.6.20, because it's an 
obvious bugfix. I've tested this patch and it's included in current -rt 
and i saw no regressions.

Acked-by: Ingo Molnar <mingo@...e.hu>

	Ingo
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