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authorFrederic Weisbecker <fweisbec@gmail.com>2013-03-27 02:18:34 +0100
committerFrederic Weisbecker <fweisbec@gmail.com>2013-04-19 13:53:14 +0200
commit0453b435df0d69dd0d8c42eb9b3015aaf0d8a032 (patch)
treea941e04d55e74cc40285834a37175a5be41c12db /Documentation/kernel-parameters.txt
parent65d798f0f9339ae2c4ebe9480e3260b33382a584 (diff)
downloadop-kernel-dev-0453b435df0d69dd0d8c42eb9b3015aaf0d8a032.zip
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nohz: Force boot CPU outside full dynticks range
The timekeeping job must be able to run early on boot because there may be some pre-SMP (and thus pre-initcalls ) components that rely on it. The IO-APIC is one such users as it tests the timer health by watching jiffies progression. Given that it happens before we know the initial online set, we can't rely on it to select a timekeeper. We need one before SMP time otherwise we simply crash on boot. To fix this and keep things simple for now, force the boot CPU outside of the full dynticks range in any case and do this early on kernel parameter parsing time. We might want a trickier solution later, expecially for aSMP architectures that need to assign housekeeping tasks to arbitrary low power CPUs. But it's still first pass KISS time for now. Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Chris Metcalf <cmetcalf@tilera.com> Cc: Christoph Lameter <cl@linux.com> Cc: Geoff Levand <geoff@infradead.org> Cc: Gilad Ben Yossef <gilad@benyossef.com> Cc: Hakan Akkan <hakanakkan@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Kevin Hilman <khilman@linaro.org> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Paul Gortmaker <paul.gortmaker@windriver.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'Documentation/kernel-parameters.txt')
-rw-r--r--Documentation/kernel-parameters.txt4
1 files changed, 2 insertions, 2 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 82365dd..887b297 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1916,8 +1916,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
nohz_full= [KNL,BOOT]
In kernels built with CONFIG_NO_HZ_FULL=y, set
the specified list of CPUs whose tick will be stopped
- whenever possible. You need to keep at least one online
- CPU outside the range to maintain the timekeeping.
+ whenever possible. The boot CPU will be forced outside
+ the range to maintain the timekeeping.
noiotrap [SH] Disables trapped I/O port accesses.
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