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Bug#1140651: linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware

Started by"Lufei Zheng" <lufei.zheng@spacemit.com>
First post2026-06-24 08:10 +0200
Last post2026-07-22 20:50 +0200
Articles 5 — 3 participants

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  Bug#1140651: linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware "Lufei Zheng" <lufei.zheng@spacemit.com> - 2026-06-24 08:10 +0200
    Bug#1140651: linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware Aurelien Jarno <aurel32@debian.org> - 2026-06-24 19:40 +0200
    Bug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small  for 80-core RISC-V hardware) "Debian Bug Tracking System" <owner@bugs.debian.org> - 2026-06-27 16:40 +0200
    Bug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small  for 80-core RISC-V hardware) "Debian Bug Tracking System" <owner@bugs.debian.org> - 2026-07-02 22:30 +0200
    Bug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small  for 80-core RISC-V hardware) "Debian Bug Tracking System" <owner@bugs.debian.org> - 2026-07-22 20:50 +0200

#93100 — Bug#1140651: linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware

From"Lufei Zheng" <lufei.zheng@spacemit.com>
Date2026-06-24 08:10 +0200
SubjectBug#1140651: linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware
Message-ID<N9oYa-rgz-11@gated-at.bofh.it>
Package: linux
Version: 6.12.86-1
Severity: important

Dear Maintainer,

The riscv64 kernel is built with CONFIG_NR_CPUS=64. On hardware with more than 64 harts, the excess CPUs are silently lost at boot.

Hardware:

  Board:   SpacemiT V100 (C2201MB1)
  Vendor:  SpacemiT (mvendorid=0x710)
  marchid: 0x8000000058000002
  mimpid:  0x4c4d900
  Arch:    riscv64, MMU sv48
  ISA:     rv64imafdcvh_zicbom_zicboz_zicntr_zicond_zicsr_zifencei
             _zihintntl_zihintpause_zihpm_zimop_zawrs_zfa_zfh_zfhmin
             _zca_zcb_zcd_zcmop_zba_zbb_zbc_zbs_zkt_zvbb_zvbc_zve32f
             _zve32x_zve64d_zve64f_zve64x_zvfh_zvfhmin_zvkb_zvkg
             _zvkned_zvknhb_zvksed_zvksh_zvkt_smaia_smstateen_ssaia
             _sscofpmf_sstc_svinval_svnapot_svpbmt
  Physical harts: 80 (hart IDs 0-39, 64-87)

Observed behaviour:

    $ nproc --all
    64

    $ cat /sys/devices/system/cpu/possible
    0-63

  16 harts are silently dropped at boot. The kernel only sees 64 CPUs.

  Boot messages:

    [    0.000000] NR_CPUS is too small for the number of ACPI tables.

  This message is repeated 16 times.

  Kernel config:

    CONFIG_SMP=y
    CONFIG_NR_CPUS=64

  Expected behaviour:

  All 80 harts should be usable. CONFIG_NR_CPUS should be raised to at least 256 for riscv64, matching the arm64 default.

Suggested fix:

In debian/config/riscv64/config, change:

    CONFIG_NR_CPUS=64

  to:

    CONFIG_NR_CPUS=256

  Workaround:

  None without recompiling the kernel.

  Thanks,
  Lufei


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#93109

FromAurelien Jarno <aurel32@debian.org>
Date2026-06-24 19:40 +0200
Message-ID<N9zJT-yrt-3@gated-at.bofh.it>
In reply to#93100
Hi,

On 2026-06-24 14:07, Lufei Zheng wrote:
> Package: linux
> Version: 6.12.86-1
> Severity: important
> 
> Dear Maintainer,
> 
> The riscv64 kernel is built with CONFIG_NR_CPUS=64. On hardware with more than 64 harts, the excess CPUs are silently lost at boot.
> 
> Hardware:
> 
>   Board:   SpacemiT V100 (C2201MB1)
>   Vendor:  SpacemiT (mvendorid=0x710)
>   marchid: 0x8000000058000002
>   mimpid:  0x4c4d900
>   Arch:    riscv64, MMU sv48
>   ISA:     rv64imafdcvh_zicbom_zicboz_zicntr_zicond_zicsr_zifencei
>              _zihintntl_zihintpause_zihpm_zimop_zawrs_zfa_zfh_zfhmin
>              _zca_zcb_zcd_zcmop_zba_zbb_zbc_zbs_zkt_zvbb_zvbc_zve32f
>              _zve32x_zve64d_zve64f_zve64x_zvfh_zvfhmin_zvkb_zvkg
>              _zvkned_zvknhb_zvksed_zvksh_zvkt_smaia_smstateen_ssaia
>              _sscofpmf_sstc_svinval_svnapot_svpbmt
>   Physical harts: 80 (hart IDs 0-39, 64-87)
>
> Observed behaviour:
> 
>     $ nproc --all
>     64
> 
>     $ cat /sys/devices/system/cpu/possible
>     0-63
> 
>   16 harts are silently dropped at boot. The kernel only sees 64 CPUs.
> 
>   Boot messages:
> 
>     [    0.000000] NR_CPUS is too small for the number of ACPI tables.
> 
>   This message is repeated 16 times.
> 
>   Kernel config:
> 
>     CONFIG_SMP=y
>     CONFIG_NR_CPUS=64
> 
>   Expected behaviour:
> 
>   All 80 harts should be usable. CONFIG_NR_CPUS should be raised to at least 256 for riscv64, matching the arm64 default.
> 
> Suggested fix:
> 
> In debian/config/riscv64/config, change:
> 
>     CONFIG_NR_CPUS=64
> 
>   to:
> 
>     CONFIG_NR_CPUS=256

No, this can't be changed as you say, because the value is not defined 
here, instead the upstream default is used. Sure we can override it in 
that file, but it would be way better if we can keep using the upstream 
default.

A MR has been submitted to change the value in the Debian kernel [1] (to 
128  instead of 256), but before doing that the default value change 
should be submitted
upstream.

Regards
Aurelien

[1] https://salsa.debian.org/kernel-team/linux/-/merge_requests/1995

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                     http://aurel32.net

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#93123 — Bug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware)

From"Debian Bug Tracking System" <owner@bugs.debian.org>
Date2026-06-27 16:40 +0200
SubjectBug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware)
Message-ID<NaCml-1j3b-35@gated-at.bofh.it>
In reply to#93100

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Your message dated Sat, 27 Jun 2026 14:34:49 +0000
with message-id <E1wdU7N-0000000DC75-3v88@fasolo.debian.org>
and subject line Bug#1140651: fixed in linux 7.1.2-1~exp1
has caused the Debian Bug report #1140651,
regarding linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
message is talking about, this may indicate a serious mail system
misconfiguration somewhere. Please contact owner@bugs.debian.org
immediately.)


-- 
1140651: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1140651
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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#93187 — Bug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware)

From"Debian Bug Tracking System" <owner@bugs.debian.org>
Date2026-07-02 22:30 +0200
SubjectBug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware)
Message-ID<NcwcN-2mmC-9@gated-at.bofh.it>
In reply to#93100

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Your message dated Thu, 02 Jul 2026 20:24:46 +0000
with message-id <E1wfNxm-00000001lSF-1hvX@fasolo.debian.org>
and subject line Bug#1140651: fixed in linux 7.0.14-1
has caused the Debian Bug report #1140651,
regarding linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
message is talking about, this may indicate a serious mail system
misconfiguration somewhere. Please contact owner@bugs.debian.org
immediately.)


-- 
1140651: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1140651
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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#93430 — Bug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware)

From"Debian Bug Tracking System" <owner@bugs.debian.org>
Date2026-07-22 20:50 +0200
SubjectBug#1140651: marked as done (linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware)
Message-ID<NjKaZ-6llf-7@gated-at.bofh.it>
In reply to#93100

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Your message dated Wed, 22 Jul 2026 18:47:06 +0000
with message-id <E1wmbyE-00000006Nme-3WqD@fasolo.debian.org>
and subject line Bug#1140651: fixed in linux 6.12.96-1
has caused the Debian Bug report #1140651,
regarding linux: CONFIG_NR_CPUS=64 too small for 80-core RISC-V hardware
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

(NB: If you are a system administrator and have no idea what this
message is talking about, this may indicate a serious mail system
misconfiguration somewhere. Please contact owner@bugs.debian.org
immediately.)


-- 
1140651: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1140651
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems

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