Re: [Qemu-devel] [PATCH] Fix phys memory client - pass guest physical address not region offset

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 2011-04-29 at 17:29 +0200, Jan Kiszka wrote:
> On 2011-04-29 17:06, Michael S. Tsirkin wrote:
> > On Thu, Apr 28, 2011 at 09:15:23PM -0600, Alex Williamson wrote:
> >> When we're trying to get a newly registered phys memory client updated
> >> with the current page mappings, we end up passing the region offset
> >> (a ram_addr_t) as the start address rather than the actual guest
> >> physical memory address (target_phys_addr_t).  If your guest has less
> >> than 3.5G of memory, these are coincidentally the same thing.  If
> 
> I think this broke even with < 3.5G as phys_offset also encodes the
> memory type while region_offset does not. So everything became RAMthis
> way, no MMIO was announced.
> 
> >> there's more, the region offset for the memory above 4G starts over
> >> at 0, so the set_memory client will overwrite it's lower memory entries.
> >>
> >> Instead, keep track of the guest phsyical address as we're walking the
> >> tables and pass that to the set_memory client.
> >>
> >> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
> > 
> > Acked-by: Michael S. Tsirkin <mst@redhat.com>
> > 
> > Given all this, can yo tell how much time does
> > it take to hotplug a device with, say, a 40G RAM guest?
> 
> Why not collect pages of identical types and report them as one chunk
> once the type changes?

Good idea, I'll see if I can code that up.  I don't have a terribly
large system to test with, but with an 8G guest, it's surprisingly not
very noticeable.  For vfio, I intend to only have one memory client, so
adding additional devices won't have to rescan everything.  The memory
overhead of keeping the list that the memory client creates is probably
also low enough that it isn't worthwhile to tear it all down if all the
devices are removed.  Thanks,

Alex