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Date: Mon, 26 Feb 2018 13:52:52 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
fweisbec@...il.com, oleg@...hat.com,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Frederic Weisbecker <frederic@...nel.org>,
Chris Metcalf <cmetcalf@...lanox.com>,
Christoph Lameter <cl@...ux.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Luiz Capitulino <lcapitulino@...hat.com>,
Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>,
Wanpeng Li <kernellwp@...il.com>,
John Stultz <john.stultz@...aro.org>,
Jonathan Corbet <corbet@....net>
Subject: [PATCH tip/core/rcu 02/20] sched/isolation: Eliminate NO_HZ_FULL_ALL
Commit 6f1982fedd59 ("sched/isolation: Handle the nohz_full= parameter")
broke CONFIG_NO_HZ_FULL_ALL=y kernels. This breakage is due to the code
under CONFIG_NO_HZ_FULL_ALL failing to invoke the shiny new housekeeping
functions. This means that rcutorture scenario TREE04 now emits RCU CPU
stall warnings due to the RCU grace-period kthreads not being awakened
at a time of their choosing, or perhaps even not at all:
[ 27.731422] rcu_bh kthread starved for 21001 jiffies! g18446744073709551369 c18446744073709551368 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=3
[ 27.731423] rcu_bh I14936 9 2 0x80080000
[ 27.731435] Call Trace:
[ 27.731440] __schedule+0x31a/0x6d0
[ 27.731442] schedule+0x31/0x80
[ 27.731446] schedule_timeout+0x15a/0x320
[ 27.731453] ? call_timer_fn+0x130/0x130
[ 27.731457] rcu_gp_kthread+0x66c/0xea0
[ 27.731458] ? rcu_gp_kthread+0x66c/0xea0
Because no one has complained about CONFIG_NO_HZ_FULL_ALL=y being broken,
I hypothesize that no one is in fact using it, other than rcutorture.
This commit therefore eliminates CONFIG_NO_HZ_FULL_ALL and updates
rcutorture's config files to instead use the nohz_full= kernel parameter
to put the desired CPUs into nohz_full mode.
Fixes: 6f1982fedd59 ("sched/isolation: Handle the nohz_full= parameter")
Reported-by: kernel test robot <xiaolong.ye@...el.com>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Chris Metcalf <cmetcalf@...lanox.com>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@...hat.com>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rik van Riel <riel@...hat.com>
Cc: Wanpeng Li <kernellwp@...il.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Jonathan Corbet <corbet@....net>
---
Documentation/timers/NO_HZ.txt | 7 -------
kernel/time/Kconfig | 10 ----------
kernel/time/tick-sched.c | 22 ++--------------------
.../selftests/rcutorture/configs/rcu/TASKS03 | 1 -
.../selftests/rcutorture/configs/rcu/TASKS03.boot | 2 +-
.../selftests/rcutorture/configs/rcu/TREE04 | 1 -
.../selftests/rcutorture/configs/rcu/TREE04.boot | 2 +-
.../selftests/rcutorture/configs/rcu/TREE07 | 1 -
8 files changed, 4 insertions(+), 42 deletions(-)
diff --git a/Documentation/timers/NO_HZ.txt b/Documentation/timers/NO_HZ.txt
index 2dcaf9adb7a7..9591092da5e0 100644
--- a/Documentation/timers/NO_HZ.txt
+++ b/Documentation/timers/NO_HZ.txt
@@ -131,13 +131,6 @@ error message, and the boot CPU will be removed from the mask. Note that
this means that your system must have at least two CPUs in order for
CONFIG_NO_HZ_FULL=y to do anything for you.
-Alternatively, the CONFIG_NO_HZ_FULL_ALL=y Kconfig parameter specifies
-that all CPUs other than the boot CPU are adaptive-ticks CPUs. This
-Kconfig parameter will be overridden by the "nohz_full=" boot parameter,
-so that if both the CONFIG_NO_HZ_FULL_ALL=y Kconfig parameter and
-the "nohz_full=1" boot parameter is specified, the boot parameter will
-prevail so that only CPU 1 will be an adaptive-ticks CPU.
-
Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded.
This is covered in the "RCU IMPLICATIONS" section below.
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index f6b5f19223d6..78eabc41eaa6 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -113,16 +113,6 @@ config NO_HZ_FULL
endchoice
-config NO_HZ_FULL_ALL
- bool "Full dynticks system on all CPUs by default (except CPU 0)"
- depends on NO_HZ_FULL
- help
- If the user doesn't pass the nohz_full boot option to
- define the range of full dynticks CPUs, consider that all
- CPUs in the system are full dynticks by default.
- Note the boot CPU will still be kept outside the range to
- handle the timekeeping duty.
-
config NO_HZ
bool "Old Idle dynticks config"
depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 29a5733eff83..ccd3782da0bf 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -405,30 +405,12 @@ static int tick_nohz_cpu_down(unsigned int cpu)
return 0;
}
-static int tick_nohz_init_all(void)
-{
- int err = -1;
-
-#ifdef CONFIG_NO_HZ_FULL_ALL
- if (!alloc_cpumask_var(&tick_nohz_full_mask, GFP_KERNEL)) {
- WARN(1, "NO_HZ: Can't allocate full dynticks cpumask\n");
- return err;
- }
- err = 0;
- cpumask_setall(tick_nohz_full_mask);
- tick_nohz_full_running = true;
-#endif
- return err;
-}
-
void __init tick_nohz_init(void)
{
int cpu, ret;
- if (!tick_nohz_full_running) {
- if (tick_nohz_init_all() < 0)
- return;
- }
+ if (!tick_nohz_full_running)
+ return;
/*
* Full dynticks uses irq work to drive the tick rescheduling on safe
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03 b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03
index c70c51d5ded1..28568b72a31b 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03
@@ -9,5 +9,4 @@ CONFIG_PREEMPT=y
CONFIG_HZ_PERIODIC=n
CONFIG_NO_HZ_IDLE=n
CONFIG_NO_HZ_FULL=y
-CONFIG_NO_HZ_FULL_ALL=y
#CHECK#CONFIG_RCU_EXPERT=n
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot
index cd2a188eeb6d..838297c58318 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot
@@ -1 +1 @@
-rcutorture.torture_type=tasks
+rcutorture.torture_type=tasks nohz_full=1
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE04 b/tools/testing/selftests/rcutorture/configs/rcu/TREE04
index 27d22695d64c..24c9f6012e35 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE04
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE04
@@ -7,7 +7,6 @@ CONFIG_PREEMPT=n
CONFIG_HZ_PERIODIC=n
CONFIG_NO_HZ_IDLE=n
CONFIG_NO_HZ_FULL=y
-CONFIG_NO_HZ_FULL_ALL=y
CONFIG_RCU_FAST_NO_HZ=y
CONFIG_RCU_TRACE=y
CONFIG_HOTPLUG_CPU=n
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot
index e34c33430447..e6071bb96c7d 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot
@@ -1 +1 @@
-rcutorture.torture_type=rcu_bh rcutree.rcu_fanout_leaf=4
+rcutorture.torture_type=rcu_bh rcutree.rcu_fanout_leaf=4 nohz_full=1-7
diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE07 b/tools/testing/selftests/rcutorture/configs/rcu/TREE07
index 0f4759f4232e..d7afb271a586 100644
--- a/tools/testing/selftests/rcutorture/configs/rcu/TREE07
+++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE07
@@ -7,7 +7,6 @@ CONFIG_PREEMPT=n
CONFIG_HZ_PERIODIC=n
CONFIG_NO_HZ_IDLE=n
CONFIG_NO_HZ_FULL=y
-CONFIG_NO_HZ_FULL_ALL=n
CONFIG_RCU_FAST_NO_HZ=n
CONFIG_RCU_TRACE=y
CONFIG_HOTPLUG_CPU=y
--
2.5.2
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