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authorFrederic Weisbecker <fweisbec@gmail.com>2012-12-18 17:32:19 +0100
committerFrederic Weisbecker <fweisbec@gmail.com>2013-03-21 15:38:33 +0100
commita831881be220358a1d28c5d95d69449fb6d623ca (patch)
tree769ab069e2837a9bd3613046110468cd87c8c3fa /kernel/time/Kconfig
parenta8d7ad52a7befbde896276d05c75c90fed48b5bf (diff)
downloadvexpress-lsk-a831881be220358a1d28c5d95d69449fb6d623ca.tar.gz
nohz: Basic full dynticks interface
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 <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: Namhyung Kim <namhyung.kim@lge.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 'kernel/time/Kconfig')
-rw-r--r--kernel/time/Kconfig19
1 files changed, 19 insertions, 0 deletions
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 24510d84efd..5a87c03e45a 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -79,6 +79,25 @@ config NO_HZ
only trigger on an as-needed basis both when the system is
busy and when the system is idle.
+config NO_HZ_EXTENDED
+ bool "Full dynticks system"
+ depends on NO_HZ && RCU_USER_QS && VIRT_CPU_ACCOUNTING_GEN && RCU_NOCB_CPU && SMP
+ select CONTEXT_TRACKING_FORCE
+ help
+ Adaptively try to shutdown the tick whenever possible, even when
+ the CPU is running tasks. Typically this requires running a single
+ task on the CPU. Chances for running tickless are maximized when
+ the task mostly runs in userspace and has few kernel activity.
+
+ You need to fill up the nohz_extended boot parameter with the
+ desired range of dynticks CPUs.
+
+ This is implemented at the expense of some overhead in user <-> kernel
+ transitions: syscalls, exceptions and interrupts. Even when it's
+ dynamically off.
+
+ Say N.
+
config HIGH_RES_TIMERS
bool "High Resolution Timer Support"
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS