Subject: [PATCH 02/10] ARM: tlb: don't perform inner-shareable invalidation for local TLB ops

From: [email-masked] (Jonathan Austin)
Date: Thu, 13 Jun 2013 18:50:03 +0100

Hi Will,

On 06/06/13 15:28, Will Deacon wrote:
> Inner-shareable TLB invalidation is typically more expensive than local
> (non-shareable) invalidation, so performing the broadcasting for
> local_flush_tlb_* operations is a waste of cycles and needlessly
> clobbers entries in the TLBs of other CPUs.
>
> This patch introduces __flush_tlb_* versions for many of the TLB
> invalidation functions, which only respect inner-shareable variants of
> the invalidation instructions. This allows us to modify the v7 SMP TLB
> flags to include *both* inner-shareable and non-shareable operations and
> then check the relevant flags depending on whether the operation is
> local or not.

I think this approach leaves us in trouble for some SMP_ON_UP cores as 
the IS versions of the instructions don't exist for them.

Is there something that should be ensuring your new __flush_tlb* 
functions don't get called for SMP_ON_UP? If not it looks like we might 
need to do some runtime patching with the ALT_SMP/ALT_UP macros...

I've commented on one of the example inline below...
>
> This gains us around 0.5% in hackbench scores for a dual-core A15, but I
> would expect this to improve as more cores (and clusters) are added to
> the equation.
>
> Reviewed-by: Catalin Marinas <[email-masked]>
> Reported-by: Albin Tonnerre <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>
> ---
>   arch/arm/include/asm/tlbflush.h | 67 ++++++++++++++++++++++++++++++++++++++---
>   arch/arm/kernel/smp_tlb.c       |  8 ++---
>   arch/arm/mm/context.c           |  6 +---
>   3 files changed, 68 insertions(+), 13 deletions(-)
>
> diff --git a/arch/arm/include/asm/tlbflush.h b/arch/arm/include/asm/tlbflush.h
> index a3625d1..55b5e18 100644
> --- a/arch/arm/include/asm/tlbflush.h
> +++ b/arch/arm/include/asm/tlbflush.h
> @@ -167,6 +167,8 @@
>   #endif
>
>   #define v7wbi_tlb_flags_smp	(TLB_WB | TLB_BARRIER | \
> +				 TLB_V6_U_FULL | TLB_V6_U_PAGE | \
> +				 TLB_V6_U_ASID | \
>   				 TLB_V7_UIS_FULL | TLB_V7_UIS_PAGE | \
>   				 TLB_V7_UIS_ASID | TLB_V7_UIS_BP)
>   #define v7wbi_tlb_flags_up	(TLB_WB | TLB_DCLEAN | TLB_BARRIER | \
> @@ -330,6 +332,21 @@ static inline void local_flush_tlb_all(void)
>   	tlb_op(TLB_V4_U_FULL | TLB_V6_U_FULL, "c8, c7, 0", zero);
>   	tlb_op(TLB_V4_D_FULL | TLB_V6_D_FULL, "c8, c6, 0", zero);
>   	tlb_op(TLB_V4_I_FULL | TLB_V6_I_FULL, "c8, c5, 0", zero);
> +
> +	if (tlb_flag(TLB_BARRIER)) {
> +		dsb();
> +		isb();
> +	}
> +}
> +
> +static inline void __flush_tlb_all(void)
> +{
> +	const int zero = 0;
> +	const unsigned int __tlb_flag = __cpu_tlb_flags;
> +
> +	if (tlb_flag(TLB_WB))
> +		dsb();
> +
>   	tlb_op(TLB_V7_UIS_FULL, "c8, c3, 0", zero);

I think we can get away with something similar to what we do in the 
cache maintenance case here, using ALT_SMP and ALT_UP to do runtime code 
patching and use TLB_V6_U_* for the UP case...

A follow on question is whether we still need to keep the *non* unified 
TLB maintenance operations (eg DTLBIALL, ITLBIALL). As far as I can see 
looking in to old TRMs, the last ARM CPU that didn't automatically treat 
those I/D ops to unified ones was ARM10, so not relevant here...

But - do some of the non-ARM cores exploit the (now deprecated) option 
to maintain these separately? Also did I miss some more obscure ARM variant?

Jonny

>
>   	if (tlb_flag(TLB_BARRIER)) {
> @@ -348,21 +365,32 @@ static inline void local_flush_tlb_mm(struct mm_struct *mm)
>   		dsb();
>
>   	if (possible_tlb_flags & (TLB_V4_U_FULL|TLB_V4_D_FULL|TLB_V4_I_FULL)) {
> -		if (cpumask_test_cpu(get_cpu(), mm_cpumask(mm))) {
> +		if (cpumask_test_cpu(smp_processor_id(), mm_cpumask(mm))) {
>   			tlb_op(TLB_V4_U_FULL, "c8, c7, 0", zero);
>   			tlb_op(TLB_V4_D_FULL, "c8, c6, 0", zero);
>   			tlb_op(TLB_V4_I_FULL, "c8, c5, 0", zero);
>   		}
> -		put_cpu();
>   	}
>
>   	tlb_op(TLB_V6_U_ASID, "c8, c7, 2", asid);
>   	tlb_op(TLB_V6_D_ASID, "c8, c6, 2", asid);
>   	tlb_op(TLB_V6_I_ASID, "c8, c5, 2", asid);
> +
> +	if (tlb_flag(TLB_BARRIER))
> +		dsb();
> +}
> +
> +static inline void __flush_tlb_mm(struct mm_struct *mm)
> +{
> +	const unsigned int __tlb_flag = __cpu_tlb_flags;
> +
> +	if (tlb_flag(TLB_WB))
> +		dsb();
> +
>   #ifdef CONFIG_ARM_ERRATA_720789
> -	tlb_op(TLB_V7_UIS_ASID, "c8, c3, 0", zero);
> +	tlb_op(TLB_V7_UIS_ASID, "c8, c3, 0", 0);
>   #else
> -	tlb_op(TLB_V7_UIS_ASID, "c8, c3, 2", asid);
> +	tlb_op(TLB_V7_UIS_ASID, "c8, c3, 2", ASID(mm));
>   #endif
>
>   	if (tlb_flag(TLB_BARRIER))
> @@ -392,6 +420,21 @@ local_flush_tlb_page(struct vm_area_struct *vma, unsigned long uaddr)
>   	tlb_op(TLB_V6_U_PAGE, "c8, c7, 1", uaddr);
>   	tlb_op(TLB_V6_D_PAGE, "c8, c6, 1", uaddr);
>   	tlb_op(TLB_V6_I_PAGE, "c8, c5, 1", uaddr);
> +
> +	if (tlb_flag(TLB_BARRIER))
> +		dsb();
> +}
> +
> +static inline void
> +__flush_tlb_page(struct vm_area_struct *vma, unsigned long uaddr)
> +{
> +	const unsigned int __tlb_flag = __cpu_tlb_flags;
> +
> +	uaddr = (uaddr & PAGE_MASK) | ASID(vma->vm_mm);
> +
> +	if (tlb_flag(TLB_WB))
> +		dsb();
> +
>   #ifdef CONFIG_ARM_ERRATA_720789
>   	tlb_op(TLB_V7_UIS_PAGE, "c8, c3, 3", uaddr & PAGE_MASK);
>   #else
> @@ -421,6 +464,22 @@ static inline void local_flush_tlb_kernel_page(unsigned long kaddr)
>   	tlb_op(TLB_V6_U_PAGE, "c8, c7, 1", kaddr);
>   	tlb_op(TLB_V6_D_PAGE, "c8, c6, 1", kaddr);
>   	tlb_op(TLB_V6_I_PAGE, "c8, c5, 1", kaddr);
> +
> +	if (tlb_flag(TLB_BARRIER)) {
> +		dsb();
> +		isb();
> +	}
> +}
> +
> +static inline void __flush_tlb_kernel_page(unsigned long kaddr)
> +{
> +	const unsigned int __tlb_flag = __cpu_tlb_flags;
> +
> +	kaddr &= PAGE_MASK;
> +
> +	if (tlb_flag(TLB_WB))
> +		dsb();
> +
>   	tlb_op(TLB_V7_UIS_PAGE, "c8, c3, 1", kaddr);
>
>   	if (tlb_flag(TLB_BARRIER)) {
> diff --git a/arch/arm/kernel/smp_tlb.c b/arch/arm/kernel/smp_tlb.c
> index 9a52a07..cc299b5 100644
> --- a/arch/arm/kernel/smp_tlb.c
> +++ b/arch/arm/kernel/smp_tlb.c
> @@ -135,7 +135,7 @@ void flush_tlb_all(void)
>   	if (tlb_ops_need_broadcast())
>   		on_each_cpu(ipi_flush_tlb_all, NULL, 1);
>   	else
> -		local_flush_tlb_all();
> +		__flush_tlb_all();
>   	broadcast_tlb_a15_erratum();
>   }
>
> @@ -144,7 +144,7 @@ void flush_tlb_mm(struct mm_struct *mm)
>   	if (tlb_ops_need_broadcast())
>   		on_each_cpu_mask(mm_cpumask(mm), ipi_flush_tlb_mm, mm, 1);
>   	else
> -		local_flush_tlb_mm(mm);
> +		__flush_tlb_mm(mm);
>   	broadcast_tlb_mm_a15_erratum(mm);
>   }
>
> @@ -157,7 +157,7 @@ void flush_tlb_page(struct vm_area_struct *vma, unsigned long uaddr)
>   		on_each_cpu_mask(mm_cpumask(vma->vm_mm), ipi_flush_tlb_page,
>   					&ta, 1);
>   	} else
> -		local_flush_tlb_page(vma, uaddr);
> +		__flush_tlb_page(vma, uaddr);
>   	broadcast_tlb_mm_a15_erratum(vma->vm_mm);
>   }
>
> @@ -168,7 +168,7 @@ void flush_tlb_kernel_page(unsigned long kaddr)
>   		ta.ta_start = kaddr;
>   		on_each_cpu(ipi_flush_tlb_kernel_page, &ta, 1);
>   	} else
> -		local_flush_tlb_kernel_page(kaddr);
> +		__flush_tlb_kernel_page(kaddr);
>   	broadcast_tlb_a15_erratum();
>   }
>
> diff --git a/arch/arm/mm/context.c b/arch/arm/mm/context.c
> index 2ac3737..62c1ec5 100644
> --- a/arch/arm/mm/context.c
> +++ b/arch/arm/mm/context.c
> @@ -134,10 +134,7 @@ static void flush_context(unsigned int cpu)
>   	}
>
>   	/* Queue a TLB invalidate and flush the I-cache if necessary. */
> -	if (!tlb_ops_need_broadcast())
> -		cpumask_set_cpu(cpu, &tlb_flush_pending);
> -	else
> -		cpumask_setall(&tlb_flush_pending);
> +	cpumask_setall(&tlb_flush_pending);
>
>   	if (icache_is_vivt_asid_tagged())
>   		__flush_icache_all();
> @@ -215,7 +212,6 @@ void check_and_switch_context(struct mm_struct *mm, struct task_struct *tsk)
>   	if (cpumask_test_and_clear_cpu(cpu, &tlb_flush_pending)) {
>   		local_flush_bp_all();
>   		local_flush_tlb_all();
> -		dummy_flush_tlb_a15_erratum();
>   	}
>
>   	atomic64_set(&per_cpu(active_asids, cpu), asid);
>