Messages in this thread Patch in this message | | | Subject | [PATCH 3 of 4] x86: pud_clear: only reload cr3 if necessary | Date | Mon, 28 Jan 2008 15:48:43 -0800 | From | Jeremy Fitzhardinge <> |
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Rather than unconditionally reloading cr3, only do so if the pud we're updating is within the active pgd.
This eliminates TLB flushes most of the time. The performance-critical uses of pud_clear are during execve and exit, but in those cases cr3 is referring to some other pagetable. The only other use of pud_clear is during a large (1Gbyte+) munmap, and those are sufficiently rare that a couple of cr3 reloads won't hurt.
Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com> --- include/asm-x86/pgtable-3level.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/include/asm-x86/pgtable-3level.h b/include/asm-x86/pgtable-3level.h --- a/include/asm-x86/pgtable-3level.h +++ b/include/asm-x86/pgtable-3level.h @@ -93,17 +93,20 @@ static inline void native_pmd_clear(pmd_ static inline void pud_clear(pud_t *pudp) { + unsigned long pgd; + set_pud(pudp, __pud(0)); /* * Pentium-II erratum A13: in PAE mode we explicitly have to flush * the TLB via cr3 if the top-level pgd is changed... * - * XXX I don't think we need to worry about this here, since - * when clearing the pud, the calling code needs to flush the - * tlb anyway. But do it now for safety's sake. - jsgf + * Make sure the pud entry we're updating is within the + * current pgd to avoid unnecessary TLB flushes. */ - write_cr3(read_cr3()); + pgd = read_cr3(); + if (__pa(pudp) >= pgd && __pa(pudp) < (pgd + sizeof(pgd_t)*PTRS_PER_PGD)) + write_cr3(pgd); } #define pud_page(pud) \
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