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sched/isolation: Eliminate NO_HZ_FULL_ALL

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Commit 6f1982fedd ("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: 6f1982fedd ("sched/isolation: Handle the nohz_full= parameter")

Reported-by: kernel test robot <xiaolong.ye@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luiz Capitulino <lcapitulino@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wanpeng Li <kernellwp@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Paul E. McKenney 2017-11-30 15:36:35 -08:00
parent 398953e62c
commit a7c8655b07
8 changed files with 4 additions and 42 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

7
Documentation/timers/NO_HZ.txt
View file

@ -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.

10
kernel/time/Kconfig
View file

@ -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

22
kernel/time/tick-sched.c
View file

@ -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

1
tools/testing/selftests/rcutorture/configs/rcu/TASKS03
View file

@ -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

2
tools/testing/selftests/rcutorture/configs/rcu/TASKS03.boot
View file

@ -1 +1 @@
rcutorture.torture_type=tasks
rcutorture.torture_type=tasks nohz_full=1

1
tools/testing/selftests/rcutorture/configs/rcu/TREE04
View file

@ -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

2
tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot
View file

@ -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

1
tools/testing/selftests/rcutorture/configs/rcu/TREE07
View file

@ -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