Re: [Qemu-devel] [PATCH v6 5/6] Inter-VM shared memory PCI device

[Avi Kivity <avi@redhat.com>]

On 06/05/2010 12:44 PM, Blue Swirl wrote:
> On Fri, Jun 4, 2010 at 9:45 PM, Cam Macdonell<cam@cs.ualberta.ca>  wrote:
>    
>> Support an inter-vm shared memory device that maps a shared-memory object as a
>> PCI device in the guest.  This patch also supports interrupts between guest by
>> communicating over a unix domain socket.  This patch applies to the qemu-kvm
>> repository.
>>
>>     -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
>>
>> Interrupts are supported between multiple VMs by using a shared memory server
>> by using a chardev socket.
>>
>>     -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
>>            [,chardev=<id>][,msi=on][,irqfd=on][,vectors=n][,role=peer|master]
>>     -chardev socket,path=<path>,id=<id>
>>
>> (shared memory server is qemu.git/contrib/ivshmem-server)
>>
>> Sample programs and init scripts are in a git repo here:
>>
>>      
> Why is this KVM specific BTW, Posix SHM is available on many
> platforms? What would happen if kvm_set_foobar functions were not
> called when KVM is not being used? Is host eventfd support essential?
>    

It's not kvm specific, it's 
atomic-ops-on-shared-memory-are-visible-as-atomic-ops specific, which is 
currently only available with kvm.  When tcg gains true smp support (and 
not just against other tcg threads) this can work with tcg as well.

I guess that needs a host with at least 32/64 bit CAS for 32/64 bit 
targets respectively, and double that if the target has DCAS.  Not sure 
how targets with ll/sc can be implemented, especially if there are 
limits as to what can go in between.

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