Re: [Qemu-devel] Re: [PATCH 2/7] Enable I/O thread and VNC threads by default

[Anthony Liguori <anthony@codemonkey.ws>]

On 02/08/2011 03:05 AM, Aurelien Jarno wrote:
> Jan Kiszka a écrit :
>    
>> On 2011-02-08 09:08, Paolo Bonzini wrote:
>>      
>>> On 02/08/2011 08:26 AM, Aurelien Jarno wrote:
>>>        
>>>> I forget to remember when we decided that AIO should be implemented on
>>>> any host OS. Any pointer?
>>>>          
>>> To be fair, I/O-heavy workloads are almost unusable without AIO.  For
>>> Window targets, they also crash under SMP due to the Windows AP
>>> watchdog.  But then TCG and SMP do not go very well together anyway.
>>>
>>> However, I think deprecating Win32 support would be a very bad idea.
>>>        
>> It would be too early at this point.
>>
>> But if Windows is once the only reason to keep tons of hardly tested
>> code paths around or to invest significant additional effort to change
>> logic or interfaces in this area, than I would prefer that step. I'm
>> hacking on IOTHREAD vs. !IOTHREAD for some weeks now, and all those
>> subtle differences are really a PITA and source of various breakages.
>>
>> People interested in that platform should finally realize that its fate
>> is coupled to reducing the #ifdefs as well as the design differences we
>> see right now and even more in the future.
>>
>>      
> The guilty here is IOTHREAD. Windows support predates IOTHREAD concept,
>    

IOTHREAD is actually just as necessary for TCG as it is for KVM.  
Otherwise, you have a signal select race that cannot be avoided.

QEMU has never "supported" Windows.  It happens to compile on Windows, 
but historically the Windows build has been non-functional for long 
periods of time and is still missing basic features (like AIO).

Regards,

Anthony Liguori

> it's just that people who introduce IOTHREAD didn't care about Windows
> support at all and added these #ifdef. Disabling Windows support because
> of that is not fair.
>
> We should probably get rid of KVM support in QEMU, so if someone has an
> idea for a cool TCG feature that can't be supported in KVM, it's the
> moment to submit it. We can add it with #ifdef, and in one year just ask
> for KVM support removal.
>
>