linux-kernel - Re: [RFC 0/2] virtio: provide a way for host to monitor critical events in the device

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Date:	Tue, 24 Jul 2012 11:26:30 +0300
From:	Dor Laor <dlaor@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
CC:	Sasha Levin <levinsasha928@...il.com>, mst@...hat.com,
	penberg@...nel.org, asias.hejun@...il.com,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, avi@...hat.com,
	anthony@...emonkey.ws, wency@...fujitsu.com
Subject: Re: [RFC 0/2] virtio: provide a way for host to monitor critical
 events in the device

On 07/24/2012 07:55 AM, Rusty Russell wrote:
> On Mon, 23 Jul 2012 22:32:39 +0200, Sasha Levin <levinsasha928@...il.com> wrote:
>> As it was discussed recently, there's currently no way for the guest to notify
>> the host about panics. Further more, there's no reasonable way to notify the
>> host of other critical events such as an OOM kill.
>
> I clearly missed the discussion.  Is this actually useful?  In practice,

Admit this is not a killer feature..

> won't you want the log from the guest?  What makes a virtual guest
> different from a physical guest?

Most times virt guest can do better than a physical OS. In that sense, 
this is where virtualization shines (live migration, hotplug for any 
virtual resource including net/block/cpu/memory/..).

There are plenty of niche but worth while small features such as the 
virtio-trace series and other that allow the host/virt-mgmt to get more 
insight into the guest w/o a need to configure the guest.

In theory guest OOM can trigger a host memory hot plug action. Again, I 
don't see it as a key feature..

>
> Guest watchdog functionality might be useful, but that's simpler to

There is already a fully emulated watchdog device in qemu.
Cheers,
Dor

> implement via a virtio watchdog device, and more effective to implement
> via a host facility that actually pings guest functionality (rather than
> the kernel).
>
> Cheers,
> Rusty.
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