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

[Jan Kiszka]

On 2011-02-08 10:05, 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,
> 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.

The TCG execution model won't scale long-term. It's already a main to
boot a quad or just dual core VM, even more when your host has at least
as many real cores. I'm sure we'll see multi-threaded TCG CPUs in the
future, and the iothread will just be one of 7, 17 or 257 threads.

Jan

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