diff options
| author | Christoph Lameter (Ampere) <cl@gentwo.org> | 2024-03-06 17:45:04 -0800 |
|---|---|---|
| committer | Catalin Marinas <catalin.marinas@arm.com> | 2024-03-07 18:18:06 +0000 |
| commit | 0499a78369adacec1af29340b71ff8dd375b4697 (patch) | |
| tree | f1ea8dc2514e7853d61e3e97e6035b45de48cecb /arch/arm64/Kconfig | |
| parent | 527db67a4d85a3400465e6d3685170a24d1deeba (diff) | |
ARM64: Dynamically allocate cpumasks and increase supported CPUs to 512
Currently defconfig selects NR_CPUS=256, but some vendors (e.g. Ampere
Computing) are planning to ship systems with 512 CPUs. So that all CPUs on
these systems can be used with defconfig, we'd like to bump NR_CPUS to 512.
Therefore this patch increases the default NR_CPUS from 256 to 512.
As increasing NR_CPUS will increase the size of cpumasks, there's a fear that
this might have a significant impact on stack usage due to code which places
cpumasks on the stack. To mitigate that concern, we can select
CPUMASK_OFFSTACK. As that doesn't seem to be a problem today with
NR_CPUS=256, we only select this when NR_CPUS > 256.
CPUMASK_OFFSTACK configures the cpumasks in the kernel to be
dynamically allocated. This was used in the X86 architecture in the
past to enable support for larger CPU configurations up to 8k cpus.
With that is becomes possible to dynamically size the allocation of
the cpu bitmaps depending on the quantity of processors detected on
bootup. Memory used for cpumasks will increase if the kernel is
run on a machine with more cores.
Further increases may be needed if ARM processor vendors start
supporting more processors. Given the current inflationary trends
in core counts from multiple processor manufacturers this may occur.
There are minor regressions for hackbench. The kernel data size
for 512 cpus is smaller with offstack than with onstack.
Benchmark results using hackbench average over 10 runs of
hackbench -s 512 -l 2000 -g 15 -f 25 -P
on Altra 80 Core
Support for 256 CPUs on stack. Baseline
7.8564 sec
Support for 512 CUs on stack.
7.8713 sec + 0.18%
512 CPUS offstack
7.8916 sec + 0.44%
Kernel size comparison:
text data filename Difference to onstack256 baseline
25755648 9589248 vmlinuz-6.8.0-rc4-onstack256
25755648 9607680 vmlinuz-6.8.0-rc4-onstack512 +0.19%
25755648 9603584 vmlinuz-6.8.0-rc4-offstack512 +0.14%
Tested-by: Eric Mackay <eric.mackay@oracle.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Christoph Lameter (Ampere) <cl@linux.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Link: https://lore.kernel.org/r/37099a57-b655-3b3a-56d0-5f7fbd49d7db@gentwo.org
[catalin.marinas@arm.com: use 'select' instead of duplicating 'config CPUMASK_OFFSTACK']
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm64/Kconfig')
| -rw-r--r-- | arch/arm64/Kconfig | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index b73d702e1e30..cdb307584d31 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -120,6 +120,7 @@ config ARM64 select CLONE_BACKWARDS select COMMON_CLK select CPU_PM if (SUSPEND || CPU_IDLE) + select CPUMASK_OFFSTACK if NR_CPUS > 256 select CRC32 select DCACHE_WORD_ACCESS select DYNAMIC_FTRACE if FUNCTION_TRACER @@ -1424,7 +1425,7 @@ config SCHED_SMT config NR_CPUS int "Maximum number of CPUs (2-4096)" range 2 4096 - default "256" + default "512" config HOTPLUG_CPU bool "Support for hot-pluggable CPUs" |