linux-kernel - Re: [PATCH v3 2/4] KVM: use simple waitqueue for vcpu->wq

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Message-ID: <562A1F29.9000101@bmw-carit.de>
Date:	Fri, 23 Oct 2015 13:51:05 +0200
From:	Daniel Wagner <daniel.wagner@...-carit.de>
To:	Paul Mackerras <paulus@...abs.org>
CC:	Peter Zijlstra <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>, <linux-rt-users@...r.kernel.org>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v3 2/4] KVM: use simple waitqueue for vcpu->wq

Hi Paul,

On 10/21/2015 01:13 PM, Peter Zijlstra wrote:
> On Wed, Oct 21, 2015 at 08:24:11PM +1100, Paul Mackerras wrote:
>> On Tue, Oct 20, 2015 at 04:00:31PM +0200, Peter Zijlstra wrote:
>>>
>>> Should we not take this opportunity to get rid of these open-coded wait
>>> loops?
>>>
>>>
>>> Does this work?
>>
>> No, on Book3S HV (POWER8) the VM hangs immediately after the kernel
>> brings up all the secondary vCPUs, and is then unkillable.  I'm not
>> sure what's wrong, although I wonder why you have TASK_IDLE rather
>> than TASK_INTERRUPTIBLE in the ___wait_event call.
> 
> This was under the assumption that INTERRUPTIBLE was because you wanted
> to avoid increasing load. Which was based on the lack of
> signal_pending() tests near there (although there might have been in the
> outermost loop which I overlooked).
> 
> If it does rely on signals, then this was obviously false and TASK_IDLE
> is indeed wrong.

If I get this right, the current patch is okay but you are going to
redactor the code? Maybe I can cherry pick your patch then and update
this patch accordingly.

cheers,
daniel
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