[PATCH v6 05/13] riscv: Only send remote fences when some other CPU is online

[Alexandre Ghiti]

On 27/03/2024 05:49, Samuel Holland wrote:
> If no other CPU is online, a local cache or TLB flush is sufficient.
> These checks can be constant-folded when SMP is disabled.
>
> Signed-off-by: Samuel Holland <samuel.holland at sifive.com>
> ---
>
> (no changes since v4)
>
> Changes in v4:
>   - New patch for v4
>
>   arch/riscv/mm/cacheflush.c | 4 +++-
>   arch/riscv/mm/tlbflush.c   | 4 +++-
>   2 files changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index d76fc73e594b..f5be1fec8191 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -21,7 +21,9 @@ void flush_icache_all(void)
>   {
>   	local_flush_icache_all();
>   
> -	if (riscv_use_sbi_for_rfence())
> +	if (num_online_cpus() < 2)
> +		return;
> +	else if (riscv_use_sbi_for_rfence())
>   		sbi_remote_fence_i(NULL);
>   	else
>   		on_each_cpu(ipi_remote_fence_i, NULL, 1);
> diff --git a/arch/riscv/mm/tlbflush.c b/arch/riscv/mm/tlbflush.c
> index da821315d43e..0901aa47b58f 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -79,7 +79,9 @@ static void __ipi_flush_tlb_all(void *info)
>   
>   void flush_tlb_all(void)
>   {
> -	if (riscv_use_sbi_for_rfence())
> +	if (num_online_cpus() < 2)
> +		local_flush_tlb_all();
> +	else if (riscv_use_sbi_for_rfence())
>   		sbi_remote_sfence_vma_asid(NULL, 0, FLUSH_TLB_MAX_SIZE, FLUSH_TLB_NO_ASID);
>   	else
>   		on_each_cpu(__ipi_flush_tlb_all, NULL, 1);


Could this be done directly in __sbi_rfence() instead?

Otherwise:

Reviewed-by: Alexandre Ghiti <alexghiti at rivosinc.com>