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@xxxxxxxxxxxxx/ 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(-) -- 2.37.0
