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

[Aurelien Jarno <aurelien@aurel32.net>]

Jan Kiszka a écrit :
> 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.
> 

And what's the issue with that? People don't always look for performance
when using QEMU. They even often try to emulate old machines (and non
x86 ones), which anyway only have one CPU. This won't change in 5 years,
the only thing is that those machines will be 5 years older.

People have to keep in mind that QEMU doesn't mean only virtualization
and doesn't mean only x86.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net