[PATCH 1/2] cpuhotplug/nohz: Remove offline cpus from nohz-idle state
Srivatsa Vaddagiri
vatsa at codeaurora.org
Thu Jan 3 21:58:38 EST 2013
Modify idle loop of arm, mips, s390, sh and x86 architectures to exit from nohz
state before dying upon hot-remove. This change is needed to avoid userspace
tools like top command from seeing a rollback in total idle time over some
sampling periods.
Additionaly, modify idle loop on all architectures supporting cpu hotplug to
have idle thread of a dying cpu die immediately after scheduler returns control
to it. There is no point in wasting time via calls to *_enter()/*_exit() before
noticing the need to die and dying.
Additional ARM specific change:
Revert commit ff081e05 ("ARM: 7457/1: smp: Fix suspicious
RCU originating from cpu_die()"), which added a RCU_NONIDLE() wrapper
around call to complete(). That wrapper is no longer needed as cpu_die() is
now called outside of a rcu_idle_enter()/exit() section. I also think that the
wait_for_completion() based wait in ARM's __cpu_die() can be replaced with a
busy-loop based one, as the wait there in general should be terminated within
few cycles.
Cc: Russell King <linux at arm.linux.org.uk>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Stephen Boyd <sboyd at codeaurora.org>
Cc: linux-arm-kernel at lists.infradead.org
Cc: Mike Frysinger <vapier at gentoo.org>
Cc: uclinux-dist-devel at blackfin.uclinux.org
Cc: Ralf Baechle <ralf at linux-mips.org>
Cc: linux-mips at linux-mips.org
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: linuxppc-dev at lists.ozlabs.org
Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
Cc: linux-s390 at vger.kernel.org
Cc: Paul Mundt <lethal at linux-sh.org>
Cc: linux-sh at vger.kernel.org
Cc: "David S. Miller" <davem at davemloft.net>
Cc: sparclinux at vger.kernel.org
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Ingo Molnar <mingo at redhat.com>
Cc: "H. Peter Anvin" <hpa at zytor.com>
Cc: x86 at kernel.org
Cc: mhocko at suse.cz
Cc: srivatsa.bhat at linux.vnet.ibm.com
Signed-off-by: Srivatsa Vaddagiri <vatsa at codeaurora.org>
---
arch/arm/kernel/process.c | 9 ++++-----
arch/arm/kernel/smp.c | 2 +-
arch/blackfin/kernel/process.c | 8 ++++----
arch/mips/kernel/process.c | 6 +++---
arch/powerpc/kernel/idle.c | 2 +-
arch/s390/kernel/process.c | 4 ++--
arch/sh/kernel/idle.c | 5 ++---
arch/sparc/kernel/process_64.c | 3 ++-
arch/x86/kernel/process.c | 5 ++---
9 files changed, 21 insertions(+), 23 deletions(-)
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index c6dec5f..254099b 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -191,11 +191,6 @@ void cpu_idle(void)
rcu_idle_enter();
ledtrig_cpu(CPU_LED_IDLE_START);
while (!need_resched()) {
-#ifdef CONFIG_HOTPLUG_CPU
- if (cpu_is_offline(smp_processor_id()))
- cpu_die();
-#endif
-
/*
* We need to disable interrupts here
* to ensure we don't miss a wakeup call.
@@ -224,6 +219,10 @@ void cpu_idle(void)
rcu_idle_exit();
tick_nohz_idle_exit();
schedule_preempt_disabled();
+#ifdef CONFIG_HOTPLUG_CPU
+ if (cpu_is_offline(smp_processor_id()))
+ cpu_die();
+#endif
}
}
diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
index 84f4cbf..a8e3b8a 100644
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -251,7 +251,7 @@ void __ref cpu_die(void)
mb();
/* Tell __cpu_die() that this CPU is now safe to dispose of */
- RCU_NONIDLE(complete(&cpu_died));
+ complete(&cpu_died);
/*
* actual CPU shutdown procedure is at least platform (if not
diff --git a/arch/blackfin/kernel/process.c b/arch/blackfin/kernel/process.c
index 3e16ad9..2bee1af 100644
--- a/arch/blackfin/kernel/process.c
+++ b/arch/blackfin/kernel/process.c
@@ -83,10 +83,6 @@ void cpu_idle(void)
while (1) {
void (*idle)(void) = pm_idle;
-#ifdef CONFIG_HOTPLUG_CPU
- if (cpu_is_offline(smp_processor_id()))
- cpu_die();
-#endif
if (!idle)
idle = default_idle;
tick_nohz_idle_enter();
@@ -98,6 +94,10 @@ void cpu_idle(void)
preempt_enable_no_resched();
schedule();
preempt_disable();
+#ifdef CONFIG_HOTPLUG_CPU
+ if (cpu_is_offline(smp_processor_id()))
+ cpu_die();
+#endif
}
}
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index a11c6f9..41102a0 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -71,13 +71,13 @@ void __noreturn cpu_idle(void)
start_critical_timings();
}
}
+ rcu_idle_exit();
+ tick_nohz_idle_exit();
+ schedule_preempt_disabled();
#ifdef CONFIG_HOTPLUG_CPU
if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map))
play_dead();
#endif
- rcu_idle_exit();
- tick_nohz_idle_exit();
- schedule_preempt_disabled();
}
}
diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index ea78761..39ad029 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -102,11 +102,11 @@ void cpu_idle(void)
ppc64_runlatch_on();
rcu_idle_exit();
tick_nohz_idle_exit();
+ schedule_preempt_disabled();
if (cpu_should_die()) {
sched_preempt_enable_no_resched();
cpu_die();
}
- schedule_preempt_disabled();
}
}
diff --git a/arch/s390/kernel/process.c b/arch/s390/kernel/process.c
index 536d645..5290556 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -66,8 +66,6 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
*/
static void default_idle(void)
{
- if (cpu_is_offline(smp_processor_id()))
- cpu_die();
local_irq_disable();
if (need_resched()) {
local_irq_enable();
@@ -95,6 +93,8 @@ void cpu_idle(void)
if (test_thread_flag(TIF_MCCK_PENDING))
s390_handle_mcck();
schedule_preempt_disabled();
+ if (cpu_is_offline(smp_processor_id()))
+ cpu_die();
}
}
diff --git a/arch/sh/kernel/idle.c b/arch/sh/kernel/idle.c
index 0c91016..f8bc2f0 100644
--- a/arch/sh/kernel/idle.c
+++ b/arch/sh/kernel/idle.c
@@ -96,9 +96,6 @@ void cpu_idle(void)
check_pgt_cache();
rmb();
- if (cpu_is_offline(cpu))
- play_dead();
-
local_irq_disable();
/* Don't trace irqs off for idle */
stop_critical_timings();
@@ -115,6 +112,8 @@ void cpu_idle(void)
rcu_idle_exit();
tick_nohz_idle_exit();
schedule_preempt_disabled();
+ if (cpu_is_offline(cpu))
+ play_dead();
}
}
diff --git a/arch/sparc/kernel/process_64.c b/arch/sparc/kernel/process_64.c
index cdb80b2..01589e7 100644
--- a/arch/sparc/kernel/process_64.c
+++ b/arch/sparc/kernel/process_64.c
@@ -105,13 +105,14 @@ void cpu_idle(void)
rcu_idle_exit();
tick_nohz_idle_exit();
+ schedule_preempt_disabled();
+
#ifdef CONFIG_HOTPLUG_CPU
if (cpu_is_offline(cpu)) {
sched_preempt_enable_no_resched();
cpu_play_dead();
}
#endif
- schedule_preempt_disabled();
}
}
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 2ed787f..3d5f142 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -331,9 +331,6 @@ void cpu_idle(void)
while (!need_resched()) {
rmb();
- if (cpu_is_offline(smp_processor_id()))
- play_dead();
-
/*
* Idle routines should keep interrupts disabled
* from here on, until they go to idle.
@@ -366,6 +363,8 @@ void cpu_idle(void)
preempt_enable_no_resched();
schedule();
preempt_disable();
+ if (cpu_is_offline(smp_processor_id()))
+ play_dead();
}
}
--
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