kernel/linux.git/include/linux/tick.h, branch v6.6.132

posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone

2024-11-14T12:19:37+00:00

[ Upstream commit b5413156bad91dc2995a5c4eab1b05e56914638a ] When cloning a new thread, its posix_cputimers are not inherited, and are cleared by posix_cputimers_init(). However, this does not clear the tick dependency it creates in tsk->tick_dep_mask, and the handler does not reach the code to clear the dependency if there were no timers to begin with. Thus if a thread has a cputimer running before clone/fork, all descendants will prevent nohz_full unless they create a cputimer of their own. Fix this by entirely clearing the tick_dep_mask in copy_process(). (There is currently no inherited state that needs a tick dependency) Process-wide timers do not have this problem because fork does not copy signal_struct as a baseline, it creates one from scratch. Fixes: b78783000d5c ("posix-cpu-timers: Migrate to use new tick dependency mask model") Signed-off-by: Ben Segall Signed-off-by: Thomas Gleixner Reviewed-by: Frederic Weisbecker Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/xm26o737bq8o.fsf@google.com Signed-off-by: Sasha Levin

tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem

2023-04-05T13:47:43+00:00

For CONFIG_NO_HZ_FULL systems, the tick_do_timer_cpu cannot be offlined. However, cpu_is_hotpluggable() still returns true for those CPUs. This causes torture tests that do offlining to end up trying to offline this CPU causing test failures. Such failure happens on all architectures. Fix the repeated error messages thrown by this (even if the hotplug errors are harmless) by asking the opinion of the nohz subsystem on whether the CPU can be hotplugged. [ Apply Frederic Weisbecker feedback on refactoring tick_nohz_cpu_down(). ] For drivers/base/ portion: Acked-by: Greg Kroah-Hartman Acked-by: Frederic Weisbecker Cc: Frederic Weisbecker Cc: "Paul E. McKenney" Cc: Zhouyi Zhou Cc: Will Deacon Cc: Marc Zyngier Cc: rcu Cc: stable@vger.kernel.org Fixes: 2987557f52b9 ("driver-core/cpu: Expose hotpluggability to the rest of the kernel") Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google)

Merge tag 'timers-nohz-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-06-28T19:22:06+00:00

Pull timers/nohz updates from Ingo Molnar: - Micro-optimize tick_nohz_full_cpu() - Optimize idle exit tick restarts to be less eager - Optimize tick_nohz_dep_set_task() to only wake up a single CPU. This reduces IPIs and interruptions on nohz_full CPUs. - Optimize tick_nohz_dep_set_signal() in a similar fashion. - Skip IPIs in tick_nohz_kick_task() when trying to kick a non-running task. - Micro-optimize tick_nohz_task_switch() IRQ flags handling to reduce context switching costs. - Misc cleanups and fixes * tag 'timers-nohz-2021-06-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: MAINTAINERS: Add myself as context tracking maintainer tick/nohz: Call tick_nohz_task_switch() with interrupts disabled tick/nohz: Kick only _queued_ task whose tick dependency is updated tick/nohz: Change signal tick dependency to wake up CPUs of member tasks tick/nohz: Only wake up a single target cpu when kicking a task tick/nohz: Update nohz_full Kconfig help tick/nohz: Update idle_exittime on actual idle exit tick/nohz: Remove superflous check for CONFIG_VIRT_CPU_ACCOUNTING_NATIVE tick/nohz: Conditionally restart tick on idle exit tick/nohz: Evaluate the CPU expression after the static key

tick/nohz: Only check for RCU deferred wakeup on user/guest entry when needed

2021-05-31T08:14:49+00:00

Checking for and processing RCU-nocb deferred wakeup upon user/guest entry is only relevant when nohz_full runs on the local CPU, otherwise the periodic tick should take care of it. Make sure we don't needlessly pollute these fast-paths as a -3% performance regression on a will-it-scale.per_process_ops has been reported so far. Fixes: 47b8ff194c1f (entry: Explicitly flush pending rcuog wakeup before last rescheduling point) Fixes: 4ae7dc97f726 (entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point) Reported-by: kernel test robot Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Paul E. McKenney Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210527113441.465489-1-frederic@kernel.org

tick/nohz: Change signal tick dependency to wake up CPUs of member tasks

2021-05-13T12:21:22+00:00

Rather than waking up all nohz_full CPUs on the system, only wake up the target CPUs of member threads of the signal. Reduces interruptions to nohz_full CPUs. Signed-off-by: Marcelo Tosatti Signed-off-by: Frederic Weisbecker Signed-off-by: Ingo Molnar Acked-by: Peter Zijlstra Link: https://lore.kernel.org/r/20210512232924.150322-8-frederic@kernel.org

tick/nohz: Evaluate the CPU expression after the static key

2021-05-13T12:21:20+00:00

When tick_nohz_full_cpu() is called with smp_processor_id(), the latter is unconditionally evaluated whether the static key is on or off. It is not necessary in the off-case though, so make sure the cpu expression is executed at the last moment. Illustrate with the following test function: int tick_nohz_test(void) { return tick_nohz_full_cpu(smp_processor_id()); } The resulting code before was: mov %gs:0x7eea92d1(%rip),%eax # smp_processor_id() fetch nopl 0x0(%rax,%rax,1) xor %eax,%eax retq cmpb $0x0,0x29d393a(%rip) # je tick_nohz_test+0x29 # jump to below eax clear mov %eax,%eax bt %rax,0x29d3936(%rip) # setb %al movzbl %al,%eax retq xor %eax,%eax retq Now it becomes: nopl 0x0(%rax,%rax,1) xor %eax,%eax retq cmpb $0x0,0x29d3871(%rip) # je tick_nohz_test+0x29 # jump to below eax clear mov %gs:0x7eea91f0(%rip),%eax # smp_processor_id() fetch, after static key mov %eax,%eax bt %rax,0x29d3866(%rip) # setb %al movzbl %al,%eax retq xor %eax,%eax retq Signed-off-by: Peter Zijlstra Signed-off-by: Frederic Weisbecker Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20210512232924.150322-2-frederic@kernel.org

rcu: Enable tick for nohz_full CPUs slow to provide expedited QS

2019-12-09T20:32:59+00:00

An expedited grace period can be stalled by a nohz_full CPU looping in kernel context. This possibility is currently handled by some carefully crafted checks in rcu_read_unlock_special() that enlist help from ksoftirqd when permitted by the scheduler. However, it is exactly these checks that require the scheduler avoid holding any of its rq or pi locks across rcu_read_unlock() without also having held them across the entire RCU read-side critical section. It would therefore be very nice if expedited grace periods could handle nohz_full CPUs looping in kernel context without such checks. This commit therefore adds code to the expedited grace period's wait and cleanup code that forces the scheduler-clock interrupt on for CPUs that fail to quickly supply a quiescent state. "Quickly" is currently a hard-coded single-jiffy delay. Signed-off-by: Paul E. McKenney

Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2019-11-26T23:42:43+00:00

Pull RCU updates from Ingo Molnar: "The main changes in this cycle were: - Dynamic tick (nohz) updates, perhaps most notably changes to force the tick on when needed due to lengthy in-kernel execution on CPUs on which RCU is waiting. - Linux-kernel memory consistency model updates. - Replace rcu_swap_protected() with rcu_prepace_pointer(). - Torture-test updates. - Documentation updates. - Miscellaneous fixes" * 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits) security/safesetid: Replace rcu_swap_protected() with rcu_replace_pointer() net/sched: Replace rcu_swap_protected() with rcu_replace_pointer() net/netfilter: Replace rcu_swap_protected() with rcu_replace_pointer() net/core: Replace rcu_swap_protected() with rcu_replace_pointer() bpf/cgroup: Replace rcu_swap_protected() with rcu_replace_pointer() fs/afs: Replace rcu_swap_protected() with rcu_replace_pointer() drivers/scsi: Replace rcu_swap_protected() with rcu_replace_pointer() drm/i915: Replace rcu_swap_protected() with rcu_replace_pointer() x86/kvm/pmu: Replace rcu_swap_protected() with rcu_replace_pointer() rcu: Upgrade rcu_swap_protected() to rcu_replace_pointer() rcu: Suppress levelspread uninitialized messages rcu: Fix uninitialized variable in nocb_gp_wait() rcu: Update descriptions for rcu_future_grace_period tracepoint rcu: Update descriptions for rcu_nocb_wake tracepoint rcu: Remove obsolete descriptions for rcu_barrier tracepoint rcu: Ensure that ->rcu_urgent_qs is set before resched IPI workqueue: Convert for_each_wq to use built-in list check rcu: Several rcu_segcblist functions can be static rcu: Remove unused function hlist_bl_del_init_rcu() Documentation: Rename rcu_node_context_switch() to rcu_note_context_switch() ...

context_tracking: Rename context_tracking_is_enabled() => context_tracking_enabled()

2019-10-29T09:01:12+00:00

Remove the superfluous "is" in the middle of the name. We want to standardize the naming so that it can be expanded through suffixes: context_tracking_enabled() context_tracking_enabled_cpu() context_tracking_enabled_this_cpu() Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Jacek Anaszewski Cc: Linus Torvalds Cc: Pavel Machek Cc: Peter Zijlstra Cc: Rafael J . Wysocki Cc: Rik van Riel Cc: Thomas Gleixner Cc: Viresh Kumar Cc: Wanpeng Li Cc: Yauheni Kaliuta Link: https://lkml.kernel.org/r/20191016025700.31277-6-frederic@kernel.org Signed-off-by: Ingo Molnar

nohz: Add TICK_DEP_BIT_RCU

2019-10-05T17:45:16+00:00

If a nohz_full CPU is looping in the kernel, the scheduling-clock tick might nevertheless remain disabled. In !PREEMPT kernels, this can prevent RCU's attempts to enlist the aid of that CPU's executions of cond_resched(), which can in turn result in an arbitrarily delayed grace period and thus an OOM. RCU therefore needs a way to enable a holdout nohz_full CPU's scheduler-clock interrupt. This commit therefore provides a new TICK_DEP_BIT_RCU value which RCU can pass to tick_dep_set_cpu() and friends to force on the scheduler-clock interrupt for a specified CPU or task. In some cases, rcutorture needs to turn on the scheduler-clock tick, so this commit also exports the relevant symbols to GPL-licensed modules. Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney