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Message-ID: <20240614075306.357861-1-liuyuntao12@huawei.com>
Date: Fri, 14 Jun 2024 07:53:06 +0000
From: Yuntao Liu <liuyuntao12@...wei.com>
To: <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
CC: <paul.walmsley@...ive.com>, <palmer@...belt.com>, <aou@...s.berkeley.edu>,
<liuyuntao12@...wei.com>
Subject: [PATCH] RISC-V: Dynamically allocate cpumasks and further increase range and default value of NR_CPUS
Currently default NR_CPUS is 64 for riscv64, since the latest QEMU virt
machine supports up to 512 CPUS, so set default NR_CPUS 512 for riscv64.
Under the promotion of RISC-V International and related chip
manufacturers, RISC-V has also begun to enter the server market, which
demands higher performance. Other major architectures (such as ARM64,
x86_64, MIPS, etc) already have a higher range, so further increase
this range up to 4096 for riscv64.
Due to the fact that increasing NR_CPUS enlarges the size of cpumasks,
there is a concern that this could significantly impact stack usage,
especially for code that allocates cpumasks on the stack. To address
this, we have the option to enable CPUMASK_OFFSTACK, which prevents
cpumasks from being allocated on the stack. we choose to enable this
feature only when NR_CPUS is greater than 512, why 512, since then
the kernel size with offstack is smaller.
vmlinux size comparison(difference to vmlinux_onstack_NR_CPUS baseline):
NR_CPUS 256 512 1024 2048 4096
onstack 19814536 19840760 19880584 19969672 20141704
offstack 19819144 19840936 19880480 19968544 20135456
difference +0.023% +0.001% -0.001% -0.001 -0.031%
is_smaller n n y y y
Signed-off-by: Yuntao Liu <liuyuntao12@...wei.com>
---
arch/riscv/Kconfig | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 0525ee2d63c7..5960713b3bf9 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -77,6 +77,7 @@ config RISCV
select CLINT_TIMER if RISCV_M_MODE
select CLONE_BACKWARDS
select COMMON_CLK
+ select CPUMASK_OFFSTACK if NR_CPUS > 512
select CPU_PM if CPU_IDLE || HIBERNATION || SUSPEND
select EDAC_SUPPORT
select FRAME_POINTER if PERF_EVENTS || (FUNCTION_TRACER && !DYNAMIC_FTRACE)
@@ -428,11 +429,11 @@ config SCHED_MC
config NR_CPUS
int "Maximum number of CPUs (2-512)"
depends on SMP
- range 2 512 if !RISCV_SBI_V01
+ range 2 4096 if !RISCV_SBI_V01
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 "512" if 64BIT
config HOTPLUG_CPU
bool "Support for hot-pluggable CPUs"
--
2.34.1
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