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


From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: [PATCH 2/7] Enable I/O thread and VNC threads by default
Date: Tue, 08 Feb 2011 03:12:22 -0600
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.15) Gecko/20101027 Lightning/1.0b1 Thunderbird/3.0.10

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.





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