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| author | Frederic Weisbecker <fweisbec@gmail.com> | 2013-03-27 02:18:34 +0100 |
|---|---|---|
| committer | Frederic Weisbecker <fweisbec@gmail.com> | 2013-04-19 13:53:14 +0200 |
| commit | 0453b435df0d69dd0d8c42eb9b3015aaf0d8a032 (patch) | |
| tree | a941e04d55e74cc40285834a37175a5be41c12db /Documentation/kernel-parameters.txt | |
| parent | 65d798f0f9339ae2c4ebe9480e3260b33382a584 (diff) | |
| download | lwn-0453b435df0d69dd0d8c42eb9b3015aaf0d8a032.tar.gz lwn-0453b435df0d69dd0d8c42eb9b3015aaf0d8a032.zip | |
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.txt | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 82365dde00a8..887b29708447 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. |