Re: [PATCH 1/4] always halt non-bsp cpu.

From: Jan Kiszka <jan.kiszka@web.de>
To: Glauber Costa <glommer@redhat.com>
Cc: kvm@vger.kernel.org, avi@redhat.com
Subject: Re: [PATCH 1/4] always halt non-bsp cpu.
Date: Wed, 03 Jun 2009 00:32:04 +0200	[thread overview]
Message-ID: <4A25A864.2070006@web.de> (raw)
In-Reply-To: <20090602220937.GY30777@poweredge.glommer>

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Glauber Costa wrote:
> On Wed, Jun 03, 2009 at 12:01:00AM +0200, Jan Kiszka wrote:
>> Glauber Costa wrote:
>>> On Tue, Jun 02, 2009 at 10:35:47PM +0200, Jan Kiszka wrote:
>>>> Glauber Costa wrote:
>>>>> This is not kvm specific, and should do fine in plain qemu
>>>> This is fine with plain qemu already. The problem, IIUC, is that
>>>> in-kernel kvm irqchip does not have a chance to remove the halted state
>>>> again. Did you test the effect of this patch on that scenario? What
>>>> makes it safe to be removed now?
>>> IIRC, the in kernel irqchip sets halted = 0 in the very beginning of
>>> the vcpu initialization.
>>>
>>> It is tested here with in-kernel irqchip and works, so probably not
>>> a problem, unless you can spot something.
>> At least your patch applied alone breaks -smp >1 here.
>>
>> But the whole management of env->halted for the in-kernel irqchip in
>> qemu-kvm is a bit hacky IMHO. Maybe it's time to rethink this. Would be
>> nice to always see a consistent halted in user space, specifically for
>> debugging purposes.
> out of curiosity: did you apply the whole series?

Meanwhile I did, but it makes no difference.

> 
> please report with it. I suspect there is a change later on that might
> make it work. Of course, this is no excuse, as I'm a huge fan of bisectability.
> If this is the case, I'll rework the series in a way that it always work.

I still suspect that dealing with halted for the in-kernel case is a bit
more tricky.

Jan

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