Re: [Xen-devel] [PATCH 1/5 TAKE 2] xenoprof: split xen x86 xenoprof code

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Fri, Nov 17, 2006 at 01:26:04PM -0600, Santos, Jose Renato G wrote:

> > > QUESTIONS for Isaku:
> > > 
> > > patch 4/5:
> > > ==========
> > > 
> > > > +struct xenoprof_shared_buffer {
> > > > +       char                                    *buffer;
> > > > +       struct xenoprof_arch_shared_buffer      arch;
> > > > +};
> > > 
> > > The arch field has no extra info for x86. Why do you need this?
> > 
> > On IA64 it is defined as
> > struct xenoprof_arch_shared_buffer {
> >         struct resource*        res;
> > };
> > 
> > On IA64, auto translated mode feature is enabled.
> > It means that page mapping from xen is based on pseudo 
> > physical address, not virtual address. Pseudo physical 
> > address used to map pages must be recorded somewhere in order 
> > to unmap.
> > I guess, if xenoprof/x86 supported auto translated guest mode 
> > something similar structure would be necessary.
> > 
> > 
>   Isaku
> 
>  I am still not convinced that we need this. Since this in the kernel
> you can always get the pseudo physical address from the virtual address,
> right? Am I missing something?

Yes, the pseudo physical address itself can be get.
The point is that the pseudo physical addresses aren't always
backed by struct page.
In such a case alloc_pages()/free_pages() can't be used, another structure
is necessary.
In fact Xen/IA64 allocates the pseudo physical address resion by
allocate_resource(&iomem_resource, ...). Not by alloc_pages().
Why doesn't Xen/IA64 use alloc_pages()?
Because it is also used for grant table foreign domain page mapping
and its size is very large sometimes. Using alloc_pages() results in OOM.
Xen/PPC seems to adopt another approach, though.


>  I applied your patches to changeset 12446 but they are failing to
> compile. I have attached the make output below
> 
>  Could you please fix this and resend?

Sorry for that. 
It should compile with CONFIG_PROFILING=y and CONFIG_OPORIFLE=y.
Anyway I'll fix and resend.
-- 
yamahata

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