subbu kl wrote:
Cam,
just a wild though about alternative approach.
Ideas are always good.
Once specific set of
address range of one guest is visible to other guest its just a matter
of DMA/single memcpy will transfer the data across.
My idea is to eliminate unnecessary copying. This introduces one.
usually non-transparent PCIe bridges(NTB) will be used for inter
processor data communication. physical PCIe NTB between two processors
just sets up a PCIe data channel with some Address translation stuffs.
So i was just wondering if we can write this non transparent bridge
(qemu PCI device) with Addrdess translation capability then guests just
can start mmap and start accessing each others memory :)
I think your concept is similar to what Anthony suggested using virtio
to export and import other VMs memory. However, RAM and shared memory
are not the same thing and having one guest access another's RAM could
confuse the guest. With the approach of mapping a BAR, the shared
memory is separate from the guest RAM but it can be mapped by the guest
processes.
Cam
~subbu
On Thu, Apr 23, 2009 at 4:11 AM, Cam Macdonell <cam@xxxxxxxxxxxxxx
<mailto:cam@xxxxxxxxxxxxxx>> wrote:
subbu kl wrote:
correct me if wrong,
can we do the sharing business by writing a non-transparent qemu
PCI device in host and guests can access each other's address
space ?
Hi Subbu,
I'm a bit confused by your question. Are you asking how this device
works or suggesting an alternative approach? I'm not sure what you
mean by a non-transparent qemu device.
Cam
~subbu
On Sun, Apr 19, 2009 at 3:56 PM, Avi Kivity <avi@xxxxxxxxxx
<mailto:avi@xxxxxxxxxx> <mailto:avi@xxxxxxxxxx
<mailto:avi@xxxxxxxxxx>>> wrote:
Cameron Macdonell wrote:
Hi Avi and Anthony,
Sorry for the top-reply, but we haven't discussed this aspect
here before.
I've been thinking about how to implement interrupts. As
far as
I can tell, unix domain sockets in Qemu/KVM are used
point-to-point with one VM being the server by specifying
"server" along with the unix: option. This works simply
for two
VMs, but I'm unsure how this can extend to multiple VMs. How
would a server VM know how many clients to wait for? How can
messages then be multicast or broadcast? Is a separate
"interrupt server" necessary?
I don't think unix provides a reliable multicast RPC. So yes, an
interrupt server seems necessary.
You could expand its role an make it a "shared memory PCI card
server", and have it also be responsible for providing the
backing
file using an SCM_RIGHTS fd. That would reduce setup
headaches for
users (setting up a file for which all VMs have permissions).
-- Do not meddle in the internals of kernels, for they are
subtle and
quick to panic.
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