Messages in this thread Patch in this message | | | Date | Fri, 7 Nov 2014 13:54:29 +0000 | From | David Vrabel <> | Subject | Re: [Xen-devel] [PATCH V2 5/5] Xen: switch to linear virtual mapped sparse p2m list |
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On 06/11/14 05:47, Juergen Gross wrote: > At start of the day the Xen hypervisor presents a contiguous mfn list > to a pv-domain. In order to support sparse memory this mfn list is > accessed via a three level p2m tree built early in the boot process. > Whenever the system needs the mfn associated with a pfn this tree is > used to find the mfn. > > Instead of using a software walked tree for accessing a specific mfn > list entry this patch is creating a virtual address area for the > entire possible mfn list including memory holes. The holes are > covered by mapping a pre-defined page consisting only of "invalid > mfn" entries. Access to a mfn entry is possible by just using the > virtual base address of the mfn list and the pfn as index into that > list. This speeds up the (hot) path of determining the mfn of a > pfn. > > Kernel build on a Dell Latitude E6440 (2 cores, HT) in 64 bit Dom0 > showed following improvements: > > Elapsed time: 32:50 -> 32:35 > System: 18:07 -> 17:47 > User: 104:00 -> 103:30
After implementing my suggestions below, please provided updated figure. They should be better.
> Tested on 64 bit dom0 and 32 bit domU. [...] > --- a/arch/x86/include/asm/xen/page.h > +++ b/arch/x86/include/asm/xen/page.h > @@ -59,6 +59,23 @@ extern int clear_foreign_p2m_mapping(struct gnttab_unmap_grant_ref *unmap_ops, > struct page **pages, unsigned int count); > extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn); > > +static inline unsigned long __pfn_to_mfn(unsigned long pfn)
These variations of pfn_to_mfn() (__pfn_to_mfn() and get_phys_to_machine() and any others), need comments explaining their differences.
Can you add __pfn_to_mfn() and the docs in a separate patch?
> + pr_notice("p2m virtual area at %p, size is %lx\n", vm.addr, vm.size);
pr_info().
> @@ -526,23 +411,83 @@ unsigned long get_phys_to_machine(unsigned long pfn) > return IDENTITY_FRAME(pfn); > } > > - topidx = p2m_top_index(pfn); > - mididx = p2m_mid_index(pfn); > - idx = p2m_index(pfn); > + ptep = lookup_address((unsigned long)(xen_p2m_addr + pfn), &level); > + BUG_ON(!ptep || level != PG_LEVEL_4K); > > /* > * The INVALID_P2M_ENTRY is filled in both p2m_*identity > * and in p2m_*missing, so returning the INVALID_P2M_ENTRY > * would be wrong. > */ > - if (p2m_top[topidx][mididx] == p2m_identity) > + if (pte_pfn(*ptep) == PFN_DOWN(__pa(p2m_identity))) > return IDENTITY_FRAME(pfn); > > - return p2m_top[topidx][mididx][idx]; > + return xen_p2m_addr[pfn];
You should test xen_p2m_addr[pfn] == INVALID_P2M_ENTRY before checking if it's an identity entry. This should skip the more expensive lookup_address() in the common case.
> bool __set_phys_to_machine(unsigned long pfn, unsigned long mfn)
I think you should map p2m_missing and p2m_identity as read-only and do the new page allocation on a write fault.
set_phys_to_machine() is used every grant map and unmap and in the common case (already allocated array page) it must be a fast and simple:
xen_p2m_addr[pfn] = mfn;
David
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