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 <atish.patra@xxxxxxx>
> ---
>  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.