Subject: Re: [PATCH] powerpc/mm: Batch tlb flush when invalidating pte entries

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 14 Nov 2016 21:38:38 +0530

"Aneesh Kumar K.V" <[email-masked]> writes:

> This will improve the task exit case, by batching tlb invalidates.
>
> Signed-off-by: Aneesh Kumar K.V <[email-masked]>
> ---
>  arch/powerpc/include/asm/book3s/64/radix.h | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
> index aec6e8ee6e27..e8b4f39e9fab 100644
> --- a/arch/powerpc/include/asm/book3s/64/radix.h
> +++ b/arch/powerpc/include/asm/book3s/64/radix.h
> @@ -147,10 +147,16 @@ static inline unsigned long radix__pte_update(struct mm_struct *mm,
>  		 * new value of pte
>  		 */
>  		new_pte = (old_pte | set) & ~clr;
> -		psize = radix_get_mmu_psize(pg_sz);
> -		radix__flush_tlb_page_psize(mm, addr, psize);
> -
> -		__radix_pte_update(ptep, 0, new_pte);
> +		/*
> +		 * If we are trying to clear the pte, we can skip
> +		 * the below sequence and batch the tlb flush. The
> +		 * tlb flush batching is done by mmu gather code
> +		 */
> +		if (new_pte) {
> +			psize = radix_get_mmu_psize(pg_sz);
> +			radix__flush_tlb_page_psize(mm, addr, psize);
> +			__radix_pte_update(ptep, 0, new_pte);
> +		}
>  	} else
>  		old_pte = __radix_pte_update(ptep, clr, set);
>  	asm volatile("ptesync" : : : "memory");

We can also avoid the ptesync I guess. BTW for transition from V=0 to
a valid pte, we are good without this patch because that is done via set_pte_at()

diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
index e8b4f39e9fab..83c77323a769 100644
--- a/arch/powerpc/include/asm/book3s/64/radix.h
+++ b/arch/powerpc/include/asm/book3s/64/radix.h
@@ -142,7 +142,6 @@ static inline unsigned long radix__pte_update(struct mm_struct *mm,
 		unsigned long new_pte;
 
 		old_pte = __radix_pte_update(ptep, ~0, 0);
-		asm volatile("ptesync" : : : "memory");
 		/*
 		 * new value of pte
 		 */
@@ -153,6 +152,7 @@ static inline unsigned long radix__pte_update(struct mm_struct *mm,
 		 * tlb flush batching is done by mmu gather code
 		 */
 		if (new_pte) {
+			asm volatile("ptesync" : : : "memory");
 			psize = radix_get_mmu_psize(pg_sz);
 			radix__flush_tlb_page_psize(mm, addr, psize);
 			__radix_pte_update(ptep, 0, new_pte);