lwn.git/kernel/time, branch v5.14-rc1

Merge branch 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

2021-07-04T19:58:33+00:00

Pull RCU updates from Paul McKenney: - Bitmap parsing support for "all" as an alias for all bits - Documentation updates - Miscellaneous fixes, including some that overlap into mm and lockdep - kvfree_rcu() updates - mem_dump_obj() updates, with acks from one of the slab-allocator maintainers - RCU NOCB CPU updates, including limited deoffloading - SRCU updates - Tasks-RCU updates - Torture-test updates * 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (78 commits) tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states rcu: Add missing __releases() annotation rcu: Remove obsolete rcu_read_unlock() deadlock commentary rcu: Improve comments describing RCU read-side critical sections rcu: Create an unrcu_pointer() to remove __rcu from a pointer srcu: Early test SRCU polling start rcu: Fix various typos in comments rcu/nocb: Unify timers rcu/nocb: Prepare for fine-grained deferred wakeup rcu/nocb: Only cancel nocb timer if not polling rcu/nocb: Delete bypass_timer upon nocb_gp wakeup rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup rcu/nocb: Allow de-offloading rdp leader rcu/nocb: Directly call __wake_nocb_gp() from bypass timer rcu: Don't penalize priority boosting when there is nothing to boost rcu: Point to documentation of ordering guarantees rcu: Make rcu_gp_cleanup() be noinline for tracing rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP ...

Merge tag 'timers-core-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2021-06-29T19:31:16+00:00

Pull timer updates from Thomas Gleixner: "Time and clocksource/clockevent related updates: Core changes: - Infrastructure to support per CPU "broadcast" devices for per CPU clockevent devices which stop in deep idle states. This allows us to utilize the more efficient architected timer on certain ARM SoCs for normal operation instead of permanentely using the slow to access SoC specific clockevent device. - Print the name of the broadcast/wakeup device in /proc/timer_list - Make the clocksource watchdog more robust against delays between reading the current active clocksource and the watchdog clocksource. Such delays can be caused by NMIs, SMIs and vCPU preemption. Handle this by reading the watchdog clocksource twice, i.e. before and after reading the current active clocksource. In case that the two watchdog reads shows an excessive time delta, the read sequence is repeated up to 3 times. - Improve the debug output and add a test module for the watchdog mechanism. - Reimplementation of the venerable time64_to_tm() function with a faster and significantly smaller version. Straight from the source, i.e. the author of the related research paper contributed this! Driver changes: - No new drivers, not even new device tree bindings! - Fixes, improvements and cleanups and all over the place" * tag 'timers-core-2021-06-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (30 commits) time/kunit: Add missing MODULE_LICENSE() time: Improve performance of time64_to_tm() clockevents: Use list_move() instead of list_del()/list_add() clocksource: Print deviation in nanoseconds when a clocksource becomes unstable clocksource: Provide kernel module to test clocksource watchdog clocksource: Reduce clocksource-skew threshold clocksource: Limit number of CPUs checked for clock synchronization clocksource: Check per-CPU clock synchronization when marked unstable clocksource: Retry clock read if long delays detected clockevents: Add missing parameter documentation clocksource/drivers/timer-ti-dm: Drop unnecessary restore clocksource/arm_arch_timer: Improve Allwinner A64 timer workaround clocksource/drivers/arm_global_timer: Remove duplicated argument in arm_global_timer clocksource/drivers/arm_global_timer: Make symbol 'gt_clk_rate_change_nb' static arm: zynq: don't disable CONFIG_ARM_GLOBAL_TIMER due to CONFIG_CPU_FREQ anymore clocksource/drivers/arm_global_timer: Implement rate compensation whenever source clock changes clocksource/drivers/ingenic: Rename unreasonable array names clocksource/drivers/timer-ti-dm: Save and restore timer TIOCP_CFG clocksource/drivers/mediatek: Ack and disable interrupts on suspend clocksource/drivers/samsung_pwm: Constify source IO memory ...

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

time/kunit: Add missing MODULE_LICENSE()

2021-06-28T05:40:23+00:00

[ mingo: MODULE_LICENSE() takes a string. ] Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar

time: Improve performance of time64_to_tm()

2021-06-24T09:51:59+00:00

The current implementation of time64_to_tm() contains unnecessary loops, branches and look-up tables. The new one uses an arithmetic-based algorithm appeared in [1] and is approximately 3x faster (YMMV). The drawback is that the new code isn't intuitive and contains many 'magic numbers' (not unusual for this type of algorithm). However, [1] justifies all those numbers and, given this function's history, the code is unlikely to need much maintenance, if any at all. Add a KUnit test for it which checks every day in a 160,000 years interval centered at 1970-01-01 against the expected result. [1] Neri, Schneider, "Euclidean Affine Functions and Applications to Calendar Algorithms". https://arxiv.org/abs/2102.06959 Signed-off-by: Cassio Neri Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210622213616.313046-1-cassio.neri@gmail.com

clockevents: Use list_move() instead of list_del()/list_add()

2021-06-22T15:16:46+00:00

Simplify the code. Reported-by: Hulk Robot Signed-off-by: Baokun Li Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210609070242.1322450-1-libaokun1@huawei.com

clocksource: Print deviation in nanoseconds when a clocksource becomes unstable

2021-06-22T14:53:17+00:00

Currently when an unstable clocksource is detected, the raw counters of that clocksource and watchdog will be printed, which can only be understood after some math calculation. So print the delta in nanoseconds as well to make it easier for humans to check the results. [ paulmck: Fix typo. ] Signed-off-by: Feng Tang Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/r/20210527190124.440372-6-paulmck@kernel.org

clocksource: Provide kernel module to test clocksource watchdog

2021-06-22T14:53:17+00:00

When the clocksource watchdog marks a clock as unstable, this might be due to that clock being unstable or it might be due to delays that happen to occur between the reads of the two clocks. It would be good to have a way of testing the clocksource watchdog's ability to distinguish between these two causes of clock skew and instability. Therefore, provide a new clocksource-wdtest module selected by a new TEST_CLOCKSOURCE_WATCHDOG Kconfig option. This module has a single module parameter named "holdoff" that provides the number of seconds of delay before testing should start, which defaults to zero when built as a module and to 10 seconds when built directly into the kernel. Very large systems that boot slowly may need to increase the value of this module parameter. This module uses hand-crafted clocksource structures to do its testing, thus avoiding messing up timing for the rest of the kernel and for user applications. This module first verifies that the ->uncertainty_margin field of the clocksource structures are set sanely. It then tests the delay-detection capability of the clocksource watchdog, increasing the number of consecutive delays injected, first provoking console messages complaining about the delays and finally forcing a clock-skew event. Unexpected test results cause at least one WARN_ON_ONCE() console splat. If there are no splats, the test has passed. Finally, it fuzzes the value returned from a clocksource to test the clocksource watchdog's ability to detect time skew. This module checks the state of its clocksource after each test, and uses WARN_ON_ONCE() to emit a console splat if there are any failures. This should enable all types of test frameworks to detect any such failures. This facility is intended for diagnostic use only, and should be avoided on production systems. Reported-by: Chris Mason Suggested-by: Thomas Gleixner Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Tested-by: Feng Tang Link: https://lore.kernel.org/r/20210527190124.440372-5-paulmck@kernel.org

clocksource: Reduce clocksource-skew threshold

2021-06-22T14:53:16+00:00

Currently, WATCHDOG_THRESHOLD is set to detect a 62.5-millisecond skew in a 500-millisecond WATCHDOG_INTERVAL. This requires that clocks be skewed by more than 12.5% in order to be marked unstable. Except that a clock that is skewed by that much is probably destroying unsuspecting software right and left. And given that there are now checks for false-positive skews due to delays between reading the two clocks, it should be possible to greatly decrease WATCHDOG_THRESHOLD, at least for fine-grained clocks such as TSC. Therefore, add a new uncertainty_margin field to the clocksource structure that contains the maximum uncertainty in nanoseconds for the corresponding clock. This field may be initialized manually, as it is for clocksource_tsc_early and clocksource_jiffies, which is copied to refined_jiffies. If the field is not initialized manually, it will be computed at clock-registry time as the period of the clock in question based on the scale and freq parameters to __clocksource_update_freq_scale() function. If either of those two parameters are zero, the tens-of-milliseconds WATCHDOG_THRESHOLD is used as a cowardly alternative to dividing by zero. No matter how the uncertainty_margin field is calculated, it is bounded below by twice WATCHDOG_MAX_SKEW, that is, by 100 microseconds. Note that manually initialized uncertainty_margin fields are not adjusted, but there is a WARN_ON_ONCE() that triggers if any such field is less than twice WATCHDOG_MAX_SKEW. This WARN_ON_ONCE() is intended to discourage production use of the one-nanosecond uncertainty_margin values that are used to test the clock-skew code itself. The actual clock-skew check uses the sum of the uncertainty_margin fields of the two clocksource structures being compared. Integer overflow is avoided because the largest computed value of the uncertainty_margin fields is one billion (10^9), and double that value fits into an unsigned int. However, if someone manually specifies (say) UINT_MAX, they will get what they deserve. Note that the refined_jiffies uncertainty_margin field is initialized to TICK_NSEC, which means that skew checks involving this clocksource will be sufficently forgiving. In a similar vein, the clocksource_tsc_early uncertainty_margin field is initialized to 32*NSEC_PER_MSEC, which replicates the current behavior and allows custom setting if needed in order to address the rare skews detected for this clocksource in current mainline. Suggested-by: Thomas Gleixner Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Acked-by: Feng Tang Link: https://lore.kernel.org/r/20210527190124.440372-4-paulmck@kernel.org

clocksource: Limit number of CPUs checked for clock synchronization

2021-06-22T14:53:16+00:00

Currently, if skew is detected on a clock marked CLOCK_SOURCE_VERIFY_PERCPU, that clock is checked on all CPUs. This is thorough, but might not be what you want on a system with a few tens of CPUs, let alone a few hundred of them. Therefore, by default check only up to eight randomly chosen CPUs. Also provide a new clocksource.verify_n_cpus kernel boot parameter. A value of -1 says to check all of the CPUs, and a non-negative value says to randomly select that number of CPUs, without concern about selecting the same CPU multiple times. However, make use of a cpumask so that a given CPU will be checked at most once. Suggested-by: Thomas Gleixner # For verify_n_cpus=1. Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Acked-by: Feng Tang Link: https://lore.kernel.org/r/20210527190124.440372-3-paulmck@kernel.org