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arm64: mm: remove dsb from update_mmu_cache

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update_mmu_cache() consists of a dsb(ishst) instruction so that new user
mappings are guaranteed to be visible to the page table walker on
exception return.

In reality this can be a very expensive operation which is rarely needed.
Removing this barrier shows a modest improvement in hackbench scores and
, in the worst case, we re-take the user fault and establish that there
was nothing to do.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Will Deacon 2015-10-06 18:46:30 +01:00 committed by Catalin Marinas
parent 28c6fbc3b4
commit 120798d2e7
1 changed files with 3 additions and 3 deletions
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6
arch/arm64/include/asm/pgtable.h
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@ -646,10 +646,10 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
unsigned long addr, pte_t *ptep)
{
/*
* set_pte() does not have a DSB for user mappings, so make sure that
* the page table write is visible.
* We don't do anything here, so there's a very small chance of
* us retaking a user fault which we just fixed up. The alternative
* is doing a dsb(ishst), but that penalises the fastpath.
*/
dsb(ishst);
}
#define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)