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Re: [Qemu-devel] Re: KVM call agenda for Feb 9

From: Anthony Liguori
Subject: Re: [Qemu-devel] Re: KVM call agenda for Feb 9
Date: Tue, 09 Feb 2010 08:18:47 -0600
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On 02/09/2010 02:52 AM, Jan Kiszka wrote:
Alexander Graf wrote:
On 09.02.2010, at 07:56, Avi Kivity wrote:
- rcuify/fine-grain qemu locks
And this should be done either way, but is probably not a short-term goal.

Indeed. We won't get around this longterm as it is a scalability
bottleneck and a killer for RT guest load. We can't push everything into
the kernel. Qemu needs a smart plan how to gradually convert its CPU and
device model to fine-grained locking.

The VCPU loops should be easy to convert to lockless operation. It's easier to do this upstream but that requires a functioning IO thread.

For the table based MMIO and PIO dispatch, RCU would be a good locking choice since these structures are rarely updated. The tricky bit is that the APIC has to be converted over to lockless before any other device can be converted because just about every device wants to inject an interrupt.


Anthony Liguori


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