| Message ID | 20121227124458.GP17584@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Dec 27, 2012 at 02:44:58PM +0200, Gleb Natapov wrote: > MMU code tries to avoid if()s HW is not able to predict reliably by using > bitwise operation to streamline code execution, but in case of a dirty bit > folding this gives us nothing since write_fault is checked right before > the folding code. Lets just piggyback onto the if() to make code more clear. > > Signed-off-by: Gleb Natapov <gleb@redhat.com> Applied, thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index 891eb6d..a7b24cf 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -249,16 +249,12 @@ retry_walk: if (!write_fault) protect_clean_gpte(&pte_access, pte); - - /* - * On a write fault, fold the dirty bit into accessed_dirty by shifting it one - * place right. - * - * On a read fault, do nothing. - */ - shift = write_fault >> ilog2(PFERR_WRITE_MASK); - shift *= PT_DIRTY_SHIFT - PT_ACCESSED_SHIFT; - accessed_dirty &= pte >> shift; + else + /* + * On a write fault, fold the dirty bit into accessed_dirty by + * shifting it one place right. + */ + accessed_dirty &= pte >> (PT_DIRTY_SHIFT - PT_ACCESSED_SHIFT); if (unlikely(!accessed_dirty)) { ret = FNAME(update_accessed_dirty_bits)(vcpu, mmu, walker, write_fault);
MMU code tries to avoid if()s HW is not able to predict reliably by using bitwise operation to streamline code execution, but in case of a dirty bit folding this gives us nothing since write_fault is checked right before the folding code. Lets just piggyback onto the if() to make code more clear. Signed-off-by: Gleb Natapov <gleb@redhat.com> -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html