Re: [PATCH v3 3/3] RISC-V: Do not invoke SBI call if cpumask is empty

[Atish Patra]

On Thu, 2019-08-22 at 03:51 +0200, Christoph Hellwig wrote:
> On Wed, Aug 21, 2019 at 05:46:44PM -0700, Atish Patra wrote:
> > SBI calls are expensive. If cpumask is empty, there is no need to
> > trap via SBI as no remote tlb flushing is required.
> > 
> > Signed-off-by: Atish Patra 
> > ---
> >  arch/riscv/mm/tlbflush.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> > index 9f58b3790baa..2bd3c418d769 100644
> > --- a/arch/riscv/mm/tlbflush.c
> > +++ b/arch/riscv/mm/tlbflush.c
> > @@ -21,6 +21,9 @@ static void __sbi_tlb_flush_range(struct cpumask
> > *cmask, unsigned long start,
> > goto issue_sfence;
> > }
> >  
> > +   if (cpumask_empty(cmask))
> > +   goto done;
> 
> I think this can even be done before the get_cpu to optimize it a
> little
> further.

Yeah. I can just return directly in this case and call get_cpu after
this. Thanks for the suggestion.


-- 
Regards,
Atish

Re: [PATCH v3 3/3] RISC-V: Do not invoke SBI call if cpumask is empty

[Christoph Hellwig]

On Wed, Aug 21, 2019 at 05:46:44PM -0700, Atish Patra wrote:
> SBI calls are expensive. If cpumask is empty, there is no need to
> trap via SBI as no remote tlb flushing is required.
> 
> Signed-off-by: Atish Patra 
> ---
>  arch/riscv/mm/tlbflush.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index 9f58b3790baa..2bd3c418d769 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -21,6 +21,9 @@ static void __sbi_tlb_flush_range(struct cpumask *cmask, 
> unsigned long start,
>   goto issue_sfence;
>   }
>  
> + if (cpumask_empty(cmask))
> + goto done;

I think this can even be done before the get_cpu to optimize it a little
further.

[PATCH v3 3/3] RISC-V: Do not invoke SBI call if cpumask is empty

[Atish Patra]

SBI calls are expensive. If cpumask is empty, there is no need to
trap via SBI as no remote tlb flushing is required.

Signed-off-by: Atish Patra 
---
 arch/riscv/mm/tlbflush.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
index 9f58b3790baa..2bd3c418d769 100644
--- a/arch/riscv/mm/tlbflush.c
+++ b/arch/riscv/mm/tlbflush.c
@@ -21,6 +21,9 @@ static void __sbi_tlb_flush_range(struct cpumask *cmask, 
unsigned long start,
goto issue_sfence;
}
 
+   if (cpumask_empty(cmask))
+   goto done;
+
if (cpumask_test_cpu(cpuid, cmask) && cpumask_weight(cmask) == 1) {
if (size <= PAGE_SIZE && size != -1)
local_flush_tlb_page(start);
-- 
2.21.0