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authorPaul E. McKenney <paulmck@kernel.org>2021-05-27 22:01:21 +0300
committerThomas Gleixner <tglx@linutronix.de>2021-06-22 17:53:16 +0300
commitfa218f1cce6ba40069c8daab8821de7e6be1cdd0 (patch)
treef3dcc2b6a10d420b22b5f5eb0613380fd76177bb /Documentation/admin-guide
parent7560c02bdffb7c52d1457fa551b9e745d4b9e754 (diff)
downloadlinux-fa218f1cce6ba40069c8daab8821de7e6be1cdd0.tar.xz
clocksource: Limit number of CPUs checked for clock synchronization
Currently, if skew is detected on a clock marked CLOCK_SOURCE_VERIFY_PERCPU, that clock is checked on all CPUs. This is thorough, but might not be what you want on a system with a few tens of CPUs, let alone a few hundred of them. Therefore, by default check only up to eight randomly chosen CPUs. Also provide a new clocksource.verify_n_cpus kernel boot parameter. A value of -1 says to check all of the CPUs, and a non-negative value says to randomly select that number of CPUs, without concern about selecting the same CPU multiple times. However, make use of a cpumask so that a given CPU will be checked at most once. Suggested-by: Thomas Gleixner <tglx@linutronix.de> # For verify_n_cpus=1. Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Feng Tang <feng.tang@intel.com> Link: https://lore.kernel.org/r/20210527190124.440372-3-paulmck@kernel.org
Diffstat (limited to 'Documentation/admin-guide')
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt10
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 995deccc28bc..9ec9ea1a51f2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -587,6 +587,16 @@
unstable. Defaults to three retries, that is,
four attempts to read the clock under test.
+ clocksource.verify_n_cpus= [KNL]
+ Limit the number of CPUs checked for clocksources
+ marked with CLOCK_SOURCE_VERIFY_PERCPU that
+ are marked unstable due to excessive skew.
+ A negative value says to check all CPUs, while
+ zero says not to check any. Values larger than
+ nr_cpu_ids are silently truncated to nr_cpu_ids.
+ The actual CPUs are chosen randomly, with
+ no replacement if the same CPU is chosen twice.
+
clearcpuid=BITNUM[,BITNUM...] [X86]
Disable CPUID feature X for the kernel. See
arch/x86/include/asm/cpufeatures.h for the valid bit