The kernel I'm working on in unstable (git://git.launchpad.net/~ubuntu-
kernel/ubuntu/+source/linux/+git/unstable) will eventually become the
Yakkety kernel. I've set NR_CPUS to 8K which is the default if you go
above 512. I've already had a request to support a platform with over 1K
cores. I'll leave it there unless we find through testing that it causes
extraordinary RAM consumption or has some other deleterious side effect.
** Changed in: linux (Ubuntu Yakkety)
Assignee: (unassigned) => Tim Gardner (timg-tpi)
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https://bugs.launchpad.net/bugs/1579205
Title:
CONFIG_NR_CPUS=256 is too low
Status in linux package in Ubuntu:
Confirmed
Status in linux source package in Yakkety:
Confirmed
Bug description:
Intel Knights Landing systems boot up to 272 processor cores. The
stock Ubuntu Linux kernel images leave processor cores above 256
disabled:
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
256/0xeb ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
257/0xef ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
258/0xf3 ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
259/0xf7 ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
260/0xfb ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
261/0xff ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
262/0x103 ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
263/0x107 ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
264/0x10b ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
265/0x10f ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
266/0x113 ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
267/0x117 ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
268/0x11b ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
269/0x11f ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
270/0x123 ignored.
[ 0.000000] ACPI: NR_CPUS/possible_cpus limit of 256 reached. Processor
271/0x127 ignored.
I'd request an increase in CONFIG_NR_CPUS to 512. This would match
Debian's default setting. For comparison, RHEL/CentOS ship with 4096.
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