Re: [PATCH 2/2] armv7 initial device passthrough support

[Mario Smarduch <mario.smarduch@huawei.com>]

On 6/15/2013 5:47 PM, Paolo Bonzini wrote:
> Il 13/06/2013 11:19, Mario Smarduch ha scritto:
>> Updated Device Passthrough Patch.
>> - optimized IRQ->CPU->vCPU binding, irq is installed once
>> - added dynamic IRQ affinity on schedule in
>> - added documentation and few other coding recommendations.
>>
>> Per earlier discussion VFIO is our target but we like
>> something earlier to work with to tackle performance
>> latency issue (some ARM related) for device passthrough 
>> while we migrate towards VFIO.
> 
> I don't think this is acceptable upstream, unfortunately.  KVM device
> assignment is deprecated and we should not add more users.
That's fine we'll work our way towards dev-tree VFIO reusing what we can
working with the community.

At this point we're more concerned with numbers and best practices as 
opposed to mechanism this part will be time consuming. 
VFIO will be more background for us.

> 
> What are the latency issues you have?

Our focus now is on IRQ latency and throughput. Right now it appears lowest latency
is 2x + exit/enter + IRQ injection overhead. We can't tolerate additional 
IPIs or deferred IRQ injection approaches. We're looking for numbers closer
to what IBMs ELI managed. Also high res timers which ARM Virt. Ext supports 
very well. Exitless interrupts which ARM handles very well too. There are
some future hw ARM interrupt enhancements coming up which may help a lot as well.

There are many other latency/perf. reqs for NFV related to RT,
essentially Guest must run near native. In the end it may turn out this
may need to be outside of main tree we'll see.

- Mario
> 
> Paolo
> 
>> - Mario