Re: KVM and Perf Counters

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Casey Jeffery wrote:
> 1. What is the best way to start and ID multiple guests? I've just
> been configuring a script to start up two of them from the
> command-line and storing an ID in the kvm_vcpu structure. The first to
> get to get to vmc_run() is designated as the primary and the other is
> then the secondary that will replicate what the primary does. 

You already have a guest ID -- the pid of the process which created the 
VM.  Is there any reason to have another ID?


> I'm open
> to ideas on automating the creation of multiple guests (with pinning
> to CPUs).
>   

You can pin using taskset(1) or sched_setaffinity(2).  I don't 
understand the problem with automating guest creation.


> 2. Where should the bulk of the buffering and synchronization be done?
> I've been putting everything in the hypervisor since it can see all
> the guests. It may make sense to put some things in the qemu code and
> make use of other IPC mechanisms for synchronization, though.
>   

Userspace is the best place.

> 3. What is the best way to deal with I/O string/string_down calls that
> handle the I/O in kvmctl.c? I would guess it will be necessary to
> buffer the memory range somewhere and pass the address of that someone
> for the secondary guest to access when it gets to that point.
>   

I'd suggest serializing everything over a socket.  That way you can run 
the primary and backup on different machines.

> 4. DMA? I haven't thought about this much yet and am using simple
> guests that don't do it. It will need to be handled eventually,
> though.
>   

Since DMA is handled by qemu, you already have a sync point.  Just tag 
the guest address and data with that sync point.

-- 
error compiling committee.c: too many arguments to function


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