linux-toradex.git/kernel/time/Kconfig, branch v5.9-rc6

posix-cpu-timers: Provide mechanisms to defer timer handling to task_work

2020-08-06T14:50:59+00:00

Running posix CPU timers in hard interrupt context has a few downsides:

 - For PREEMPT_RT it cannot work as the expiry code needs to take
   sighand lock, which is a 'sleeping spinlock' in RT. The original RT
   approach of offloading the posix CPU timer handling into a high
   priority thread was clumsy and provided no real benefit in general.

 - For fine grained accounting it's just wrong to run this in context of
   the timer interrupt because that way a process specific CPU time is
   accounted to the timer interrupt.

 - Long running timer interrupts caused by a large amount of expiring
   timers which can be created and armed by unpriviledged user space.

There is no hard requirement to expire them in interrupt context.

If the signal is targeted at the task itself then it won't be delivered
before the task returns to user space anyway. If the signal is targeted at
a supervisor process then it might be slightly delayed, but posix CPU
timers are inaccurate anyway due to the fact that they are tied to the
tick.

Provide infrastructure to schedule task work which allows splitting the
posix CPU timer code into a quick check in interrupt context and a thread
context expiry and signal delivery function. This has to be enabled by
architectures as it requires that the architecture specific KVM
implementation handles pending task work before exiting to guest mode.

Signed-off-by: Thomas Gleixner 
Signed-off-by: Ingo Molnar 
Reviewed-by: Oleg Nesterov 
Acked-by: Peter Zijlstra (Intel) 
Link: https://lore.kernel.org/r/20200730102337.783470146@linutronix.de

treewide: Add SPDX license identifier - Makefile/Kconfig

2019-05-21T08:50:46+00:00

Add SPDX license identifiers to all Make/Kconfig files which:

 - Have no license information of any form

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

  GPL-2.0-only

Signed-off-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

time: Move CONTEXT_TRACKING to kernel/time/Kconfig

2019-01-15T10:16:41+00:00

Both CONTEXT_TRACKING and CONTEXT_TRACKING_FORCE are currently defined
in kernel/rcu/kconfig, which might have made sense at some point, but
no longer does given that RCU refers to neither of these Kconfig options.

Therefore move them to kernel/time/Kconfig, where the rest of the
NO_HZ_FULL Kconfig options live.

Signed-off-by: Paul E. McKenney 
Signed-off-by: Thomas Gleixner 
Cc: Frederic Weisbecker 
Link: https://lkml.kernel.org/r/20181220170525.GA12579@linux.ibm.com

clocksource: Provide clocksource_arch_init()

2018-10-04T21:00:24+00:00

Architectures have extra archdata in the clocksource, e.g. for VDSO
support. There are no sanity checks or general initializations for this
available. Add support for that.

Signed-off-by: Thomas Gleixner 
Acked-by: Andy Lutomirski 
Acked-by: John Stultz 
Cc: Peter Zijlstra 
Cc: Matt Rickard 
Cc: Stephen Boyd 
Cc: Florian Weimer 
Cc: "K. Y. Srinivasan" 
Cc: Vitaly Kuznetsov 
Cc: devel@linuxdriverproject.org
Cc: virtualization@lists.linux-foundation.org
Cc: Paolo Bonzini 
Cc: Arnd Bergmann 
Cc: Juergen Gross 
Link: https://lkml.kernel.org/r/20180917130706.973042587@linutronix.de

sched/isolation: Eliminate NO_HZ_FULL_ALL

2018-02-15T23:40:37+00:00

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 
Signed-off-by: Paul E. McKenney 
Cc: Frederic Weisbecker 
Cc: Thomas Gleixner 
Cc: Chris Metcalf 
Cc: Christoph Lameter 
Cc: Linus Torvalds 
Cc: Luiz Capitulino 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Rik van Riel 
Cc: Wanpeng Li 
Cc: Ingo Molnar 
Cc: John Stultz 
Cc: Jonathan Corbet

sched/isolation: Make CONFIG_NO_HZ_FULL select CONFIG_CPU_ISOLATION

2017-12-18T12:46:42+00:00

CONFIG_NO_HZ_FULL doesn't make sense without CONFIG_CPU_ISOLATION. In
fact enabling the first without the second is a regression as nohz_full=
boot parameter gets silently ignored.

Besides this unnatural combination hangs RCU gp kthread when running
rcutorture for reasons that are not yet fully understood:

	rcu_preempt kthread starved for 9974 jiffies! g4294967208
	+c4294967207 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x402 ->cpu=0
	rcu_preempt     I 7464     8      2 0x80000000
	Call Trace:
		__schedule+0x493/0x620
		schedule+0x24/0x40
		schedule_timeout+0x330/0x3b0
		? preempt_count_sub+0xea/0x140
		? collect_expired_timers+0xb0/0xb0
		rcu_gp_kthread+0x6bf/0xef0

This commit therefore makes NO_HZ_FULL select CPU_ISOLATION, which
prevents all these bad behaviours.

Reported-by: kernel test robot 
Signed-off-by: Paul E. McKenney 
Signed-off-by: Frederic Weisbecker 
Cc: Chris Metcalf 
Cc: Christoph Lameter 
Cc: John Stultz 
Cc: Linus Torvalds 
Cc: Luiz Capitulino 
Cc: Mike Galbraith 
Cc: Peter Zijlstra 
Cc: Rik van Riel 
Cc: Thomas Gleixner 
Cc: Wanpeng Li 
Fixes: 5c4991e24c69 ("sched/isolation: Split out new CONFIG_CPU_ISOLATION=y config from CONFIG_NO_HZ_FULL")
Link: http://lkml.kernel.org/r/1513275507-29200-2-git-send-email-frederic@kernel.org
Signed-off-by: Ingo Molnar

timekeeping: Remove CONFIG_GENERIC_TIME_VSYSCALL_OLD

2017-11-14T10:20:25+00:00

As of d4d1fc61eb38f (ia64: Update fsyscall gettime to use modern
vsyscall_update)the last user of CONFIG_GENERIC_TIME_VSYSCALL_OLD
have been updated, the legacy support for old-style vsyscall
implementations can be removed from the timekeeping code.

(Thanks again to Tony Luck for helping remove the last user!)

[jstultz: Commit message rework]

Signed-off-by: Miroslav Lichvar 
Signed-off-by: John Stultz 
Signed-off-by: Thomas Gleixner 
Cc: Prarit Bhargava 
Cc: Tony Luck 
Cc: Richard Cochran 
Cc: Stephen Boyd 
Link: https://lkml.kernel.org/r/1510613491-16695-1-git-send-email-john.stultz@linaro.org

kernel/time/Kconfig: Fix typo in comment

2017-11-02T11:50:34+00:00

Fix typo in Kconfig comment text.

Signed-off-by: Randy Dunlap 
Signed-off-by: Thomas Gleixner 
Cc: John Stultz 
Cc: Stephen Boyd 
Cc: Jiri Kosina 
Link: https://lkml.kernel.org/r/0e586dd4-2b27-864e-c252-bc72df52fd01@infradead.org

rcu: Remove nohz_full full-system-idle state machine

2017-06-09T01:52:39+00:00

The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013
by commit 0edd1b1784cb ("nohz_full: Add full-system-idle state machine"),
but has not been used.  This commit therefore removes it.

If it turns out to be needed later, this commit can always be reverted.

Signed-off-by: Paul E. McKenney 
Cc: Frederic Weisbecker 
Cc: Rik van Riel 
Cc: Ingo Molnar 
Acked-by: Linus Torvalds

rcu: Drop RCU_USER_QS in favor of NO_HZ_FULL

2015-07-06T20:52:18+00:00

The RCU_USER_QS Kconfig parameter is now just a synonym for NO_HZ_FULL,
so this commit eliminates RCU_USER_QS, replacing all uses with NO_HZ_FULL.

Reported-by: Frederic Weisbecker 
Signed-off-by: Paul E. McKenney 
Acked-by: Frederic Weisbecker