[PATCH] riscv: Raise default NR_CPUS for 64BIT to 256
Vivian Wang <[email protected]>
| Newsgroups | dev.linux.lists.spacemit,org.infradead.lists.linux-riscv,org.kernel.vger.linux-kernel |
|---|---|
| Message-ID | <[email protected]> |
SpacemiT has already produced a 80-core RVA23 RISC-V server [1], and going further back, the dual-socket SG2042-based Sophgo Pisces has 128 cores (although that had some issues achieving mainline support). Therefore, an NR_CPUS of 64 is not enough. Raise default NR_CPUS to 256 for 64BIT (when !RISCV_SBI_V01, since very old firmware can't support more than 64 cores). The number was picked as a power of two that is at least double the known max. I believe this should be the right balance between not wasting too much memory and not having to touch this too often. Ubuntu has already been shipping NR_CPUS=512 for riscv64. We have also been testing NR_CPUS=256 internally at ISCAS and found negligible performance impact and no ill effects. Reported-by: Lufei Zheng <[email protected]> Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1140651 # [1] Suggested-by: Han Gao <[email protected]> Signed-off-by: Vivian Wang <[email protected]> --- arch/riscv/Kconfig | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 3f0a647218e4..c0a6992933e4 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -454,7 +454,8 @@ config NR_CPUS range 2 32 if RISCV_SBI_V01 && 32BIT range 2 64 if RISCV_SBI_V01 && 64BIT default "32" if 32BIT - default "64" if 64BIT + default "64" if RISCV_SBI_V01 && 64BIT + default "256" if !RISCV_SBI_V01 && 64BIT config HOTPLUG_CPU bool "Support for hot-pluggable CPUs" --- base-commit: ab9de95c9cf952332ab79453b4b5d1bfca8e514f change-id: 20260625-riscv-more-nr-cpus-8158dbb4640c Best regards, -- Vivian Wang <[email protected]>