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John Stultz dc491596f6 timekeeping: Rework frequency adjustments to work better w/ nohz 
The existing timekeeping_adjust logic has always been complicated
to understand. Further, since it was developed prior to NOHZ becoming
common, its not surprising it performs poorly when NOHZ is enabled.

Since Miroslav pointed out the problematic nature of the existing code
in the NOHZ case, I've tried to refactor the code to perform better.

The problem with the previous approach was that it tried to adjust
for the total cumulative error using a scaled dampening factor. This
resulted in large errors to be corrected slowly, while small errors
were corrected quickly. With NOHZ the timekeeping code doesn't know
how far out the next tick will be, so this results in bad
over-correction to small errors, and insufficient correction to large
errors.

Inspired by Miroslav's patch, I've refactored the code to try to
address the correction in two steps.

1) Check the future freq error for the next tick, and if the frequency
error is large, try to make sure we correct it so it doesn't cause
much accumulated error.

2) Then make a small single unit adjustment to correct any cumulative
error that has collected over time.

This method performs fairly well in the simulator Miroslav created.

Major credit to Miroslav for pointing out the issue, providing the
original patch to resolve this, a simulator for testing, as well as
helping debug and resolve issues in my implementation so that it
performed closer to his original implementation.

Cc: Miroslav Lichvar <mlichvar@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Reported-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
2014-07-23 15:01:56 -07:00
..
debug kdb: Use ktime_get_ts() 2014-06-12 16:18:45 +02:00
events Oleg Nesterov found and fixed a bug in the perf/ftrace/uprobes code where 2014-07-03 18:37:25 -07:00
gcov gcov: add support for GCC 4.9 2014-06-10 15:34:46 -07:00
irq genirq: Fix memory leak when calling irq_free_hwirqs() 2014-07-05 21:42:08 +02:00
locking Merge branch 'locking-urgent-for-linus.patch' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-06-21 07:06:02 -10:00
power x86, kaslr: boot-time selectable with hibernation 2014-06-16 23:30:44 +02:00
printk kernel/printk/printk.c: revert "printk: enable interrupts before calling console_trylock_for_printk()" 2014-07-03 09:21:54 -07:00
rcu Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next 2014-06-03 12:57:53 -07:00
sched Merge branch 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2014-06-12 19:42:15 -07:00
time timekeeping: Rework frequency adjustments to work better w/ nohz 2014-07-23 15:01:56 -07:00
trace ftrace: Provide trace clocks monotonic 2014-07-23 15:01:55 -07:00
.gitignore Ignore generated file kernel/x509_certificate_list 2013-12-10 18:21:34 +00:00
acct.c sched: Make task->start_time nanoseconds based 2014-07-23 10:18:05 -07:00
async.c
audit.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2014-06-12 14:27:40 -07:00
audit.h audit: Use struct net not pid_t to remember the network namespce to reply in 2014-03-20 10:10:53 -04:00
audit_tree.c inotify: Fix reporting of cookies for inotify events 2014-02-18 11:17:17 +01:00
audit_watch.c inotify: Fix reporting of cookies for inotify events 2014-02-18 11:17:17 +01:00
auditfilter.c Merge git://git.infradead.org/users/eparis/audit 2014-04-12 12:38:53 -07:00
auditsc.c auditsc: audit_krule mask accesses need bounds checking 2014-06-10 08:44:40 -07:00
backtracetest.c kernel/backtracetest.c: replace no level printk by pr_info() 2014-06-04 16:54:14 -07:00
bounds.c mm: do not allocate page->ptl dynamically, if spinlock_t fits to long 2013-12-20 12:25:45 -08:00
capability.c fs,userns: Change inode_capable to capable_wrt_inode_uidgid 2014-06-10 13:57:22 -07:00
cgroup.c cgroup: fix a race between cgroup_mount() and cgroup_kill_sb() 2014-06-30 10:16:26 -04:00
cgroup_freezer.c cgroup: remove css_parent() 2014-05-16 13:22:48 -04:00
compat.c kernel/compat.c: use sizeof() instead of sizeof 2014-06-04 16:54:19 -07:00
configs.c
context_tracking.c x86/kprobes: Fix build errors and blacklist context_track_user 2014-06-14 09:07:44 +02:00
cpu.c More ACPI and power management updates for 3.16-rc1 2014-06-12 13:14:19 -07:00
cpu_pm.c
cpuset.c cpuset: break kernfs active protection in cpuset_write_resmask() 2014-07-01 16:42:28 -04:00
crash_dump.c
cred.c
delayacct.c delayacct: Remove braindamaged type conversions 2014-07-23 10:18:06 -07:00
dma.c
elfcore.c
exec_domain.c kernel/exec_domain.c: code clean-up 2014-06-04 16:54:15 -07:00
exit.c signals: mv {dis,}allow_signal() from sched.h/exit.c to signal.[ch] 2014-06-06 16:08:11 -07:00
extable.c asmlinkage: Make main_extable_sort_needed visible 2014-02-13 18:13:22 -08:00
fork.c sched: Make task->start_time nanoseconds based 2014-07-23 10:18:05 -07:00
freezer.c libata, freezer: avoid block device removal while system is frozen 2013-12-19 13:50:32 -05:00
futex.c Merge branch 'next' (accumulated 3.16 merge window patches) into master 2014-06-08 11:31:16 -07:00
futex_compat.c compat: Get rid of (get|put)_compat_time(val|spec) 2014-02-02 14:09:12 -08:00
groups.c kernel/groups.c: remove return value of set_groups 2014-04-03 16:21:05 -07:00
hung_task.c kernel/hung_task.c: convert simple_strtoul to kstrtouint 2014-06-04 16:54:15 -07:00
irq_work.c perf/x86: Warn to early_printk() in case irq_work is too slow 2014-02-21 21:49:07 +01:00
jump_label.c
kallsyms.c kernel: use macros from compiler.h instead of __attribute__((...)) 2014-04-07 16:36:11 -07:00
kcmp.c
Kconfig.freezer
Kconfig.hz kernel: remove CONFIG_USE_GENERIC_SMP_HELPERS 2013-11-15 09:32:22 +09:00
Kconfig.locks locking/rwlocks: Introduce 'qrwlocks' - fair, queued rwlocks 2014-06-06 07:58:28 +02:00
Kconfig.preempt
kexec.c kexec: save PG_head_mask in VMCOREINFO 2014-06-23 16:47:43 -07:00
kmod.c signals: change wait_for_helper() to use kernel_sigaction() 2014-06-06 16:08:12 -07:00
kprobes.c kprobes: Show blacklist entries via debugfs 2014-04-24 10:26:41 +02:00
ksysfs.c kobject: Make support for uevent_helper optional. 2014-04-25 12:00:49 -07:00
kthread.c kthread: fix return value of kthread_create() upon SIGKILL. 2014-06-04 16:53:51 -07:00
latencytop.c kernel/latencytop.c: convert seq_printf to seq_puts 2014-06-04 16:54:15 -07:00
Makefile time/timers: Move all time(r) related files into kernel/time 2014-06-23 11:22:35 +02:00
module-internal.h
module.c Most of this is cleaning up various driver sysfs permissions so we can 2014-06-11 16:09:14 -07:00
module_signing.c
notifier.c kprobes, notifier: Use NOKPROBE_SYMBOL macro in notifier 2014-04-24 10:26:39 +02:00
nsproxy.c
padata.c padata: Fix wrong usage of rcu_dereference() 2013-12-05 21:28:42 +08:00
panic.c kernel/panic.c: add "crash_kexec_post_notifiers" option for kdump after panic_notifers 2014-06-06 16:08:12 -07:00
params.c param: hand arguments after -- straight to init 2014-04-28 11:48:34 +09:30
pid.c
pid_namespace.c pid_namespace: pidns_get() should check task_active_pid_ns() != NULL 2014-04-02 16:20:21 -07:00
profile.c kernel/profile.c: use static const char instead of static char 2014-06-06 16:08:13 -07:00
ptrace.c kernel/compat: convert to COMPAT_SYSCALL_DEFINE 2014-03-06 15:35:10 +01:00
range.c
reboot.c kernel/reboot.c: convert simple_strtoul to kstrtoint 2014-06-04 16:54:15 -07:00
relay.c Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2014-04-12 14:49:50 -07:00
res_counter.c kernel/res_counter.c: replace simple_strtoull by kstrtoull 2014-06-04 16:54:15 -07:00
resource.c resources: Clarify sanity check message 2014-05-23 10:47:21 -06:00
seccomp.c Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2014-06-12 14:27:40 -07:00
signal.c signals: introduce kernel_sigaction() 2014-06-06 16:08:12 -07:00
smp.c CPU hotplug, smp: flush any pending IPI callbacks before CPU offline 2014-06-23 16:47:43 -07:00
smpboot.c
smpboot.h
softirq.c Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu into core/rcu 2014-05-22 11:36:10 +02:00
stacktrace.c
stop_machine.c kernel/stop_machine.c: kernel-doc warning fix 2014-06-04 16:54:15 -07:00
sys.c sched: Consolidate open coded implementations of nice level frobbing into nice_to_rlimit() and rlimit_to_nice() 2014-05-22 11:16:36 +02:00
sys_ni.c sys_sgetmask/sys_ssetmask: add CONFIG_SGETMASK_SYSCALL 2014-06-04 16:54:14 -07:00
sysctl.c kernel/watchdog.c: print traces for all cpus on lockup detection 2014-06-23 16:47:44 -07:00
sysctl_binary.c kernel/sysctl_binary.c: use scnprintf() instead of snprintf() 2013-11-13 12:09:33 +09:00
system_certificates.S KEYS: correct alignment of system_certificate_list content in assembly file 2013-12-10 18:25:28 +00:00
system_keyring.c KEYS: correct alignment of system_certificate_list content in assembly file 2013-12-10 18:25:28 +00:00
task_work.c
taskstats.c genetlink: only pass array to genl_register_family_with_ops() 2013-11-19 16:39:05 -05:00
test_kprobes.c
torture.c torture: Remove __init from torture_init_begin/end 2014-05-14 09:46:30 -07:00
tracepoint.c tracing: syscall_regfunc() should not skip kernel threads 2014-06-21 00:15:26 -04:00
tsacct.c sched: Make task->start_time nanoseconds based 2014-07-23 10:18:05 -07:00
uid16.c
up.c smp: Rename __smp_call_function_single() to smp_call_function_single_async() 2014-02-24 14:47:15 -08:00
user-return-notifier.c
user.c kernel/user.c: drop unused field 'files' from user_struct 2014-06-04 16:54:16 -07:00
user_namespace.c kernel/user_namespace.c: kernel-doc/checkpatch fixes 2014-06-06 16:08:13 -07:00
utsname.c
utsname_sysctl.c sysctl: convert use of typedef ctl_table to struct ctl_table 2014-06-06 16:08:16 -07:00
watchdog.c kernel/watchdog.c: print traces for all cpus on lockup detection 2014-06-23 16:47:44 -07:00
workqueue.c workqueue: zero cpumask of wq_numa_possible_cpumask on init 2014-07-07 09:56:48 -04:00
workqueue_internal.h workqueue: rename manager_mutex to attach_mutex 2014-05-20 10:59:32 -04:00