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

[Alex Williamson]

On Fri, 2011-04-29 at 18:34 +0300, Michael S. Tsirkin wrote:
> On Fri, Apr 29, 2011 at 05:29:06PM +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 <address@hidden>
> > > 
> > > Acked-by: Michael S. Tsirkin <address@hidden>
> > > 
> > > 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?
> 
> Sure, but before we bother to optimize this, is this too slow?

At a set_memory call per 4k page, it's probably worthwhile to factor in
some simply optimizations.  My set_memory callback was being hit 10^6
times.  Thanks,

Alex