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

[Jan Kiszka]

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).

Jan

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