linux-kernel - [PATCH 06/27] nohz: Basic full dynticks interface

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Date:	Sat, 29 Dec 2012 17:42:45 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH 06/27] nohz: Basic full dynticks interface

Start with a very simple interface to define full dynticks CPU:
use a boot time option defined cpumask through the "full_nohz="
kernel parameter.

Make sure you keep at least one CPU outside this range to handle
the timekeeping.

Also full_nohz= must match rcu_nocb= value.

Suggested-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Alessio Igor Bogani <abogani@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Chris Metcalf <cmetcalf@...era.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Geoff Levand <geoff@...radead.org>
Cc: Gilad Ben Yossef <gilad@...yossef.com>
Cc: Hakan Akkan <hakanakkan@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 include/linux/tick.h     |    7 +++++++
 kernel/time/Kconfig      |    9 +++++++++
 kernel/time/tick-sched.c |   23 +++++++++++++++++++++++
 3 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 553272e..2d4f6f0 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -157,6 +157,13 @@ static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
 static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
 # endif /* !NO_HZ */
 
+#ifdef CONFIG_NO_HZ_FULL
+int tick_nohz_full_cpu(int cpu);
+#else
+static inline int tick_nohz_full_cpu(int cpu) { return 0; }
+#endif
+
+
 # ifdef CONFIG_CPU_IDLE_GOV_MENU
 extern void menu_hrtimer_cancel(void);
 # else
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index 8601f0d..dc6381d 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -70,6 +70,15 @@ 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_FULL
+       bool "Full tickless system"
+       depends on NO_HZ && RCU_USER_QS && VIRT_CPU_ACCOUNTING_GEN && RCU_NOCB_CPU && SMP
+       select CONTEXT_TRACKING_FORCE
+       help
+         Try to be tickless everywhere, not just in idle. (You need
+	 to fill up the full_nohz_mask boot parameter).
+
+
 config HIGH_RES_TIMERS
 	bool "High Resolution Timer Support"
 	depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index ad0e6fa..fac9ba4 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -142,6 +142,29 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
 	profile_tick(CPU_PROFILING);
 }
 
+#ifdef CONFIG_NO_HZ_FULL
+static cpumask_var_t full_nohz_mask;
+bool have_full_nohz_mask;
+
+int tick_nohz_full_cpu(int cpu)
+{
+	if (!have_full_nohz_mask)
+		return 0;
+
+	return cpumask_test_cpu(cpu, full_nohz_mask);
+}
+
+/* Parse the boot-time nohz CPU list from the kernel parameters. */
+static int __init tick_nohz_full_setup(char *str)
+{
+	alloc_bootmem_cpumask_var(&full_nohz_mask);
+	have_full_nohz_mask = true;
+	cpulist_parse(str, full_nohz_mask);
+	return 1;
+}
+__setup("full_nohz=", tick_nohz_full_setup);
+#endif
+
 /*
  * NOHZ - aka dynamic tick functionality
  */
-- 
1.7.5.4

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