[linuxsh-dev] kernel tlb miss optimization query

[peter g. <pga...@li...>]

Sorry for monopolising this group.

Mr Stuart Menefy has provided a patch for optimising the tlb miss exception handling. 
I am using the 2.5.13 kernel, downloaded from sourceforge here. 
Changes to the files pgalloc.h and pgtable.h defining pmd_populate_kernel and pmd_page_kernel cause patch rejections.

In short,
The original pgalloc.h has

    #define pmd_populate(mm, pmd, pte) set_pmd(pmd, __pmd(_PAGE_TABLE + __pa(pte)))

The 2.5.13 version defines pmd_populate_kernel as previously, but change pmd_populate to

    set_pmd(pmd, __pmd(_PAGE_TABLE + page_to_phys(pte)))

The tlb update patch defines pmd_populate to be

    set_pmd(pmd, __pmd(pte))

similarly, the original pgtable.h has

    #define pmd_page(pmd) ( (ul) _va(pmd_val) & PAGE_MASK)

The 2.5.13 changes this to pmd_page_kernel, and redefines pmd_page to be 

    (phys_to_page(pmd_val(pmd)))

However the tlb update patch redefines pmd_page(pmd) to be ((ul) __va(pmd_val(pmd)))

I wish to know what the TLB patch does to kernel page tables in general and what should happen here. Also would a possibly less efficient implementation that only changes entry.S to do the assembly language equivalent of 

   pgd_offset(current->mm, address)
   pmd_offset(pdg, address)
   pte_offset(pmd, address)
   update ptel
   ldtlb
   rte

be likely to work?

Cheers


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