From: Avi Kivity <avi@qumranet.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Dor Laor <dor.laor@qumranet.com>,
kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: [kvm-devel] [RFC] Deferred interrupt handling.
Date: Wed, 18 Jul 2007 19:46:13 +0300 [thread overview]
Message-ID: <469E43D5.70802@qumranet.com> (raw)
In-Reply-To: <20070718174736.0baf6d0e@the-village.bc.nu>
Alan Cox wrote:
>> What if we will force the specific device to the end of the list. Once
>> IRQ_NONE was returned by the other devices, we will mask the irq,
>> forward the irq to the guest, issue a timer for 1msec. Motivation:
>> 1msec is long enough for the guest to ack the irq + host unmask the irq
>>
>
> It makes no difference. The deadlock isn't fixable by timing hacks.
> Consider the following sequence
>
>
> Guest0 - blocked on I/O
>
> IRQ14 from your hardware
> Block IRQ14
> Sent to guest (guest is blocked)
>
> IRQ14 from hard disk
> Ignored (as blocked)
>
> Deadlock
>
IMO the only reasonable solution is to disallow interrupt forwarding
with shared irqs. If someone later comes up with a bright idea, we can
implement it. Otherwise the problem will solve itself with hardware
moving to msi.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
WARNING: multiple messages have this Message-ID (diff)
From: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
To: Alan Cox <alan-qBU/x9rampVanCEyBjwyrvXRex20P6io@public.gmane.org>
Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [RFC] Deferred interrupt handling.
Date: Wed, 18 Jul 2007 19:46:13 +0300 [thread overview]
Message-ID: <469E43D5.70802@qumranet.com> (raw)
In-Reply-To: <20070718174736.0baf6d0e-v58gJUvfdfWUJIigds3554dd74u8MsAO@public.gmane.org>
Alan Cox wrote:
>> What if we will force the specific device to the end of the list. Once
>> IRQ_NONE was returned by the other devices, we will mask the irq,
>> forward the irq to the guest, issue a timer for 1msec. Motivation:
>> 1msec is long enough for the guest to ack the irq + host unmask the irq
>>
>
> It makes no difference. The deadlock isn't fixable by timing hacks.
> Consider the following sequence
>
>
> Guest0 - blocked on I/O
>
> IRQ14 from your hardware
> Block IRQ14
> Sent to guest (guest is blocked)
>
> IRQ14 from hard disk
> Ignored (as blocked)
>
> Deadlock
>
IMO the only reasonable solution is to disallow interrupt forwarding
with shared irqs. If someone later comes up with a bright idea, we can
implement it. Otherwise the problem will solve itself with hardware
moving to msi.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
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next prev parent reply other threads:[~2007-07-18 16:46 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-07-18 9:53 [RFC] Deferred interrupt handling Or Sagi
2007-07-18 9:53 ` Or Sagi
2007-07-18 11:30 ` Alan Cox
2007-07-18 11:30 ` Alan Cox
2007-07-18 16:36 ` [kvm-devel] " Dor Laor
2007-07-18 16:36 ` Dor Laor
2007-07-18 16:47 ` [kvm-devel] " Alan Cox
2007-07-18 16:47 ` Alan Cox
2007-07-18 16:46 ` Avi Kivity [this message]
2007-07-18 16:46 ` Avi Kivity
2007-07-18 16:57 ` [kvm-devel] " Alan Cox
2007-07-18 16:57 ` Alan Cox
2007-07-18 16:57 ` [kvm-devel] " Avi Kivity
2007-07-18 16:57 ` Avi Kivity
2007-07-18 17:14 ` [kvm-devel] " Alan Cox
2007-07-18 17:14 ` Alan Cox
2007-07-18 17:09 ` [kvm-devel] " Dor Laor
2007-07-18 17:09 ` Dor Laor
2007-07-18 17:33 ` [kvm-devel] " Alan Cox
2007-07-18 17:33 ` Alan Cox
2007-07-18 21:29 ` [kvm-devel] " Dor Laor
2007-07-18 21:29 ` Dor Laor
2007-07-18 21:46 ` [kvm-devel] " Alan Cox
2007-07-18 21:46 ` Alan Cox
2007-07-25 14:18 ` [kvm-devel] " Pavel Machek
2007-07-25 14:18 ` Pavel Machek
2007-07-18 22:23 ` [kvm-devel] " Or Sagi
2007-07-18 22:23 ` Or Sagi
2007-07-18 19:14 ` [kvm-devel] " Lennart Sorensen
2007-07-18 19:14 ` Lennart Sorensen
2007-07-19 9:23 ` [kvm-devel] " Avi Kivity
2007-07-19 9:23 ` Avi Kivity
2007-07-19 13:17 ` [kvm-devel] " Lennart Sorensen
2007-07-19 13:17 ` Lennart Sorensen
2007-07-19 13:38 ` [kvm-devel] " Avi Kivity
2007-07-19 13:38 ` Avi Kivity
2007-07-19 16:23 ` [kvm-devel] " Lennart Sorensen
2007-07-19 16:23 ` Lennart Sorensen
2007-07-18 15:57 ` Lennart Sorensen
2007-07-18 15:57 ` Lennart Sorensen
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