On Tue, Jan 2, 2024 at 11:01 PM Samuel Holland
<samuel.holland@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
>
> 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 47c485bc7df0..f7933ae88a55 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 2f18fe6fc4f3..37b3c93e3c30 100644
> --- a/arch/riscv/mm/tlbflush.c
> +++ b/arch/riscv/mm/tlbflush.c
> @@ -73,7 +73,9 @@ 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);
> --
> 2.42.0
>
on_each_cpu() already deals correctly with a single online cpu, the
only thing to optimize here is the SBI rfence. So I'd move this new
test in sbi_remote_sfence_vma_asid() and sbi_remote_fence_i() to avoid
the superfluous M-mode entry when only one cpu is online by checking
the cpumask. And since sbi_remote_fence_i() is used in another
function (flush_icache_mm()), we could also take advantage of this
optimization when only the local cpu must be flushed.
