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Date: Mon, 07 Feb 2011 15:02:03 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: [PATCH 2/7] Enable I/O thread and VNC threads
	by default
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>, Marcelo Tosatti <mtosatti@redhat.com>, qemu-devel@nongnu.org, Anthony Liguori <aliguori@linux.vnet.ibm.com>, Paul Brook <paul@codesourcery.com>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>, Arun Bharadwaj <arun@linux.vnet.ibm.com>

On 02/07/2011 11:10 AM, Jan Kiszka wrote:
> On 2011-02-07 17:23, Paolo Bonzini wrote:
>    
>> On 02/07/2011 05:03 PM, Marcelo Tosatti wrote:
>>      
>>> Is there any other issue that prevents turning CONFIG_IOTHREAD on by
>>> default?
>>>        
>> I think Windows support.
>>
>> Signal support is actually easy because we can "hack" the IPI as
>> "suspend the VCPU thread+do work in the iothread context+resume the VCPU
>> thread" (the IPI handler doesn't longjmp).
>>
>> Threading primitives support is tricky but not hard (there is lots of
>> code around, especially if you can make assumptions such as "always hold
>> the mutex while signaling a cond. variable").
>>      
> !CONFIG_IOTHREAD code is doomed to bitrot once we switch to default
> iothread mode. So if Windows support is not converted to a threading
> model with moderate differences to POSIX, it will likely bitrot a well.
> Therefore, conversion should be started rather sooner than later (by
> someone interested in that platform).
>    

As far as I'm concerned, Windows support is already deprecated as noone 
has stepped up to enhance it or support for a number of years now.  We 
shouldn't remove existing code that supports it or refuse to take 
reasonable patches but if enabling IO thread by default breaks it, so be it.

Regards,

Anthony Liguori

> Jan
>
>