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Date: Sat, 05 Mar 2011 18:11:41 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: [Qemu-devel] Re: kvm crashes with spice while loading qxl
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To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: kvm@vger.kernel.org, qemu-devel <qemu-devel@nongnu.org>, xming <xmingske@gmail.com>, Jan Kiszka <jan.kiszka@web.de>, Avi Kivity <avi@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>

On 03/05/2011 05:35 PM, Marcelo Tosatti wrote:
> TCG and KVM execution behaviour can become more
> similar wrt locking by dropping qemu_global_mutex during generation and
> execution of TBs.
>
> Of course for memory or PIO accesses from vcpu context qemu_global_mutex
> must be acquired.

-icount already has most of the machinery needed for this.

At this point, I think people interested in TCG should choose between 
staying with legacy and gaining a bit more speed for uniprocessor 
simulation, or following KVM with a more complex architecture and 
finer-grained locking---but also a more future-proof design.

BTW, I'll post soon patches for iothread -icount that work (at least in 
my tests), are much simpler than anything I posted so far, and hopefully 
will show that iothread is not fundamentally incompatible with anything 
(and in fact can simplify things much more than complicate them).

> With that in place, it becomes easier to justify further improvements
> regarding parallelization, such as using a read-write lock for
> l1_phys_map / phys_page_find_alloc.

Or URCU (userspace RCU), too.

Paolo