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powerpc/pseries/mobility: set NMI watchdog factor during an LPM

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During an LPM, while the memory transfer is in progress on the arrival
side, some latencies are generated when accessing not yet transferred
pages on the arrival side. Thus, the NMI watchdog may be triggered too
frequently, which increases the risk to hit an NMI interrupt in a bad
place in the kernel, leading to a kernel panic.

Disabling the Hard Lockup Watchdog until the memory transfer could be a
too strong work around, some users would want this timeout to be
eventually triggered if the system is hanging even during an LPM.

Introduce a new sysctl variable nmi_watchdog_factor. It allows to apply
a factor to the NMI watchdog timeout during an LPM. Just before the CPUs
are stopped for the switchover sequence, the NMI watchdog timer is set
to watchdog_thresh + factor%

A value of 0 has no effect. The default value is 200, meaning that the
NMI watchdog is set to 30s during LPM (based on a 10s watchdog_thresh
value). Once the memory transfer is achieved, the factor is reset to 0.

Setting this value to a high number is like disabling the NMI watchdog
during an LPM.

Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220713154729.80789-5-ldufour@linux.ibm.com
This commit is contained in:
Laurent Dufour
2022-07-13 17:47:29 +02:00
committed by Michael Ellerman
parent f5e74e8360
commit 118b136693
2 changed files with 55 additions and 0 deletions
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12
Documentation/admin-guide/sysctl/kernel.rst
View File

@@ -592,6 +592,18 @@ to the guest kernel command line (see
Documentation/admin-guide/kernel-parameters.rst).
nmi_wd_lpm_factor (PPC only)
============================
Factor to apply to the NMI watchdog timeout (only when ``nmi_watchdog`` is
set to 1). This factor represents the percentage added to
``watchdog_thresh`` when calculating the NMI watchdog timeout during an
LPM. The soft lockup timeout is not impacted.
A value of 0 means no change. The default value is 200 meaning the NMI
watchdog is set to 30s (based on ``watchdog_thresh`` equal to 10).
numa_balancing
==============