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[v5,0/4] Extending NMI watchdog during LPM

Message ID 20220713154729.80789-1-ldufour@linux.ibm.com
Headers show
Series Extending NMI watchdog during LPM | expand

Message

Laurent Dufour July 13, 2022, 3:47 p.m. UTC 
When a partition is transferred, once it arrives at the destination node,
the partition is active but much of its memory must be transferred from the
start node.

It depends on the activity in the partition, but the more CPU the partition
has, the more memory to be transferred is likely to be. This causes latency
when accessing pages that need to be transferred, and often, for large
partitions, it triggers the NMI watchdog.

The NMI watchdog causes the CPU stack to dump where it appears to be
stuck. In this case, it does not bring much information since it can happen
during any memory access of the kernel.

In addition, the NMI interrupt mechanism is not secure and can generate a
dump system in the event that the interruption is taken while MSR[RI]=0.

Depending on the LPAR size and load, it may be interesting to extend the
NMI watchdog timer during the LPM.

That's configurable through sysctl with the new introduced variable
(specific to powerpc) nmi_watchdog_factor. This value represents the
percentage added to watchdog_tresh to set the NMI watchdog timeout during a
LPM.

Changes in V5 (no functional changes in this version):
Patch 4/4:
 - fixing typos and grammar issues reported by Randy.
 - Renaming sysctl value from nmi_watchdog_factor to nmi_wd_lpm_factor as
   per Nick request

V4:
https://lore.kernel.org/linuxppc-dev/20220712143202.23144-1-ldufour@linux.ibm.com/

Laurent Dufour (4):
  powerpc/mobility: wait for memory transfer to complete
  watchdog: export lockup_detector_reconfigure
  powerpc/watchdog: introduce a NMI watchdog's factor
  pseries/mobility: set NMI watchdog factor during an LPM

 Documentation/admin-guide/sysctl/kernel.rst | 12 +++
 arch/powerpc/include/asm/nmi.h              |  2 +
 arch/powerpc/kernel/watchdog.c              | 21 ++++-
 arch/powerpc/platforms/pseries/mobility.c   | 91 ++++++++++++++++++++-
 include/linux/nmi.h                         |  2 +
 kernel/watchdog.c                           | 21 +++--
 6 files changed, 141 insertions(+), 8 deletions(-)

Comments

Michael Ellerman July 29, 2022, 1:02 p.m. UTC | #1 
On Wed, 13 Jul 2022 17:47:25 +0200, Laurent Dufour wrote:
> When a partition is transferred, once it arrives at the destination node,
> the partition is active but much of its memory must be transferred from the
> start node.
> 
> It depends on the activity in the partition, but the more CPU the partition
> has, the more memory to be transferred is likely to be. This causes latency
> when accessing pages that need to be transferred, and often, for large
> partitions, it triggers the NMI watchdog.
> 
> [...]

Applied to powerpc/next.

[1/4] powerpc/mobility: wait for memory transfer to complete
      https://git.kernel.org/powerpc/c/882c0d1704cf61df13f01933269202d51e74b9f3
[2/4] watchdog: export lockup_detector_reconfigure
      https://git.kernel.org/powerpc/c/7c56a8733d0a2a4be2438a7512566e5ce552fccf
[3/4] powerpc/watchdog: introduce a NMI watchdog's factor
      https://git.kernel.org/powerpc/c/f5e74e836097d1004077390717d4bd95d4a2c27a
[4/4] pseries/mobility: set NMI watchdog factor during an LPM
      https://git.kernel.org/powerpc/c/118b1366930c8c833b8b36abef657f40d4e26610

cheers