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nohz: Basic full dynticks interface

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For extreme usecases such as Real Time or HPC, having
the ability to shutdown the tick when a single task runs
on a CPU is a desired feature:

* Reducing the amount of interrupts improves throughput
for CPU-bound tasks. The CPU is less distracted from its
real job, from an execution time and from the cache point
of views.

* This also improve latency response as we have less critical
sections.

Start with introducing a very simple interface to define
full dynticks CPU: use a boot time option defined cpumask
through the "nohz_extended=" kernel parameter. CPUs that
are part of this range will have their tick shutdown
whenever possible: provided they run a single task and
they don't do kernel activity that require the periodic
tick. These details will be later documented in
Documentation/*

An online CPU must be kept outside this range to handle the
timekeeping.

Suggested-by: Paul E. McKenney <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Chris Metcalf <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Geoff Levand <[email protected]>
Cc: Gilad Ben Yossef <[email protected]>
Cc: Hakan Akkan <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Kevin Hilman <[email protected]>
Cc: Li Zhong <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Thomas Gleixner <[email protected]>
This commit is contained in:
Frederic Weisbecker 2012-12-18 17:32:19 +01:00
commit a831881be2
4 changed files with 94 additions and 0 deletions
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6
Documentation/kernel-parameters.txt
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@ -1913,6 +1913,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
Valid arguments: on, off
Default: on
nohz_extended= [KNL,BOOT]
In kernels built with CONFIG_NO_HZ_EXTENDED=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.
noiotrap [SH] Disables trapped I/O port accesses.
noirqdebug [X86-32] Disables the code which attempts to detect and