Hello,
currently my code (and all the examples I could find in the Xen source
code) uses a single page mem_event ring buffer, using code along the
lines of:
/* Map the ring page */
unsigned long ring_pfn;
xc_get_hvm_param(xci_, domain_, HVM_PARAM_ACCESS_RING_PFN, &ring_pfn);
unsigned long mmap_pfn = ring_pfn;
ringPage_ = xc_map_foreign_batch(xci_, domain_, PROT_READ | PROT_WRITE,
&mmap_pfn, 1);
if (mmap_pfn & XEN_DOMCTL_PFINFO_XTAB) {
/* Map failed, populate ring page */
if (xc_domain_populate_physmap_exact(xci_, domain_,
1, 0, 0, &ring_pfn))
return SOME_ERROR;
mmap_pfn = ring_pfn;
ringPage = xc_map_foreign_batch(xci_, domain_,
PROT_READ | PROT_WRITE,
&mmap_pfn, 1);
if (mmap_pfn & XEN_DOMCTL_PFINFO_XTAB)
return SOME_OTHER ERROR;
}
Could I safely use more than one page for the ring buffer (passing
''2''
as the last parameter of xc_map_foreign_batch(), and so on), or am I
limited to 1 page by design?
Thanks,
Razvan Cojocaru
On Tue, Mar 05, 2013 at 03:21:38PM +0200, Razvan Cojocaru wrote:> Hello, > > currently my code (and all the examples I could find in the Xen > source code) uses a single page mem_event ring buffer, using code > along the lines of: > > /* Map the ring page */ > unsigned long ring_pfn; > xc_get_hvm_param(xci_, domain_, HVM_PARAM_ACCESS_RING_PFN, &ring_pfn); > > unsigned long mmap_pfn = ring_pfn; > ringPage_ = xc_map_foreign_batch(xci_, domain_, PROT_READ | PROT_WRITE, > &mmap_pfn, 1); > > if (mmap_pfn & XEN_DOMCTL_PFINFO_XTAB) { > > /* Map failed, populate ring page */ > if (xc_domain_populate_physmap_exact(xci_, domain_, > 1, 0, 0, &ring_pfn)) > return SOME_ERROR; > > mmap_pfn = ring_pfn; > ringPage = xc_map_foreign_batch(xci_, domain_, > PROT_READ | PROT_WRITE, > &mmap_pfn, 1); > > if (mmap_pfn & XEN_DOMCTL_PFINFO_XTAB) > return SOME_OTHER ERROR; > } > > Could I safely use more than one page for the ring buffer (passing > ''2'' as the last parameter of xc_map_foreign_batch(), and so on), or > am I limited to 1 page by design?You should be able to as many as you want. Are you hitting any particular issues?> > > Thanks, > Razvan Cojocaru > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel >
>> Could I safely use more than one page for the ring buffer (passing >> ''2'' as the last parameter of xc_map_foreign_batch(), and so on), or >> am I limited to 1 page by design? > > You should be able to as many as you want. Are you hitting any > particular issues?Haven''t tried it yet, I''ve just noticed that all the example code using it hardcoded ''1'' as the number of pages it asks for, xenaccess.c has a comment to the effect of "/* Map the ring _page_ */", and so on. Thanks, Razvan Cojocaru
>> Could I safely use more than one page for the ring buffer (passing >> ''2'' as the last parameter of xc_map_foreign_batch(), and so on), or >> am I limited to 1 page by design? > > You should be able to as many as you want. Are you hitting any > particular issues?Actually, now that I''ve tried it, xc_domain_decrease_reservation_exact(xch, domain, RING_PAGES, 0, &ring_pfn) is failing for any RING_PAGES > 1. Any ideas? Thanks, Razvan Cojocaru
> > Hello, > > currently my code (and all the examples I could find in the Xen source > code) uses a single page mem_event ring buffer, using code along the > lines of: > > /* Map the ring page */ > unsigned long ring_pfn; > xc_get_hvm_param(xci_, domain_, HVM_PARAM_ACCESS_RING_PFN, &ring_pfn); > > unsigned long mmap_pfn = ring_pfn; > ringPage_ = xc_map_foreign_batch(xci_, domain_, PROT_READ | PROT_WRITE, > &mmap_pfn, 1); > > if (mmap_pfn & XEN_DOMCTL_PFINFO_XTAB) { > > /* Map failed, populate ring page */ > if (xc_domain_populate_physmap_exact(xci_, domain_, > 1, 0, 0, &ring_pfn)) > return SOME_ERROR; > > mmap_pfn = ring_pfn; > ringPage = xc_map_foreign_batch(xci_, domain_, > PROT_READ | PROT_WRITE, > &mmap_pfn, 1); > > if (mmap_pfn & XEN_DOMCTL_PFINFO_XTAB) > return SOME_OTHER ERROR; > } > > Could I safely use more than one page for the ring buffer (passing ''2'' > as the last parameter of xc_map_foreign_batch(), and so on), or am I > limited to 1 page by design?You would have to change Xen itself to also view the N pages as a contiguous region in the virtual address space. I think vmap has been recently added for that purpose, but I know nothing about its limitations (cc''ing Jan). You would also want to retain the old interface and add a new domctl for N-page ring setup. And some refactoring of all the places where that sequence of calls needed for setup is repeated. And a pony ;) Thanks! Andres> > > Thanks, > Razvan Cojocaru
>> Could I safely use more than one page for the ring buffer (passing ''2'' >> as the last parameter of xc_map_foreign_batch(), and so on), or am I >> limited to 1 page by design? > > You would have to change Xen itself to also view the N pages as a contiguous region in the virtual address space. I think vmap has been recently added for that purpose, but I know nothing about its limitations (cc''ing Jan). > > You would also want to retain the old interface and add a new domctl for N-page ring setup. And some refactoring of all the places where that sequence of calls needed for setup is repeated. And a pony ;)Ah, that''s what I thought. Will ask management to budget for the pony :) Thanks, Razvan Cojocaru