On Mon, 31 Oct 2022 12:26:05 PDT (-0700), atishp@xxxxxxxxxxxxxx wrote:
On Mon, Oct 31, 2022 at 12:12 PM Conor Dooley <conor@xxxxxxxxxx> wrote:On Fri, Oct 28, 2022 at 04:19:29PM -0700, Atish Patra wrote: > It is useless to issue remote fences if there is a single core > available. It becomes a bottleneck for sbi based rfences where > we will be making those ECALLs for no reason. Early code patching > because of static calls end up in this path. > > Signed-off-by: Atish Patra <atishp@xxxxxxxxxxxx> Hey Atish, This doesn't apply for me to either fixes or for-next. What branch does it apply to? Thanks, Conor. > --- > arch/riscv/mm/cacheflush.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c > index f10cb47eac3a..7fafc8c26505 100644 > --- a/arch/riscv/mm/cacheflush.c > +++ b/arch/riscv/mm/cacheflush.c > @@ -19,6 +19,10 @@ void flush_icache_all(void) > { > local_flush_icache_all(); > > + /* No need to issue remote fence if only 1 cpu is online */ > + if (num_online_cpus() == 1) > + return; > + > if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence()) > sbi_remote_fence_i(NULL); > else > -- > 2.34.1 >Sorry I forgot to specify the dependencies for this patch. This patch is based on Anup's IPI series [1] as I assumed the IPI series would go first. I can rebase on top of the master if required. However, the issue will manifest only after Jisheng's patch[2] which moved the sbi_init to earlier and introduced the static key in the paging_init path. [1] https://patchwork.kernel.org/project/linux-riscv/patch/20220820065446.389788-8-apatel@xxxxxxxxxxxxxxxx/ [2] https://lore.kernel.org/lkml/20220716115059.3509-1-jszhang@xxxxxxxxxx/
IMO we should just stop issuing the SBI remote fences at all, with the code to do IPI-based fences we're just adding complexity for the slow case.
