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Merge tag 'rcu.2022.01.09a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

Browse Source 
Pull RCU updates from Paul McKenney:

 - Documentation updates, perhaps most notably Neil Brown's writeup of
   the reference-counting analogy to RCU.

 - Expedited grace-period cleanups.

 - Remove CONFIG_RCU_FAST_NO_HZ due to lack of valid users. I have asked
   around, posted a blog entry, and sent this series to LKML without
   result.

 - Miscellaneous fixes.

 - RCU callback offloading updates, perhaps most notably Frederic
   Weisbecker's updates allowing CPUs booted in the de-offloaded state
   to be offloaded at runtime.

 - nolibc fixes from Willy Tarreau and Anmar Faizi, but also including
   Mark Brown's addition of gettid().

 - RCU Tasks Trace fixes, including changes that increase the
   scalability of call_rcu_tasks_trace() for the BPF folks (Martin Lau
   and KP Singh).

 - Various fixes including those from Wander Lairson Costa and Li
   Zhijian.

 - Fixes plus addition of tests for the increased call_rcu_tasks_trace()
   scalability.

* tag 'rcu.2022.01.09a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (87 commits)
  rcu/nocb: Merge rcu_spawn_cpu_nocb_kthread() and rcu_spawn_one_nocb_kthread()
  rcu/nocb: Allow empty "rcu_nocbs" kernel parameter
  rcu/nocb: Create kthreads on all CPUs if "rcu_nocbs=" or "nohz_full=" are passed
  rcu/nocb: Optimize kthreads and rdp initialization
  rcu/nocb: Prepare nocb_cb_wait() to start with a non-offloaded rdp
  rcu/nocb: Remove rcu_node structure from nocb list when de-offloaded
  rcu-tasks: Use fewer callbacks queues if callback flood ends
  rcu-tasks: Use separate ->percpu_dequeue_lim for callback dequeueing
  rcu-tasks: Use more callback queues if contention encountered
  rcu-tasks: Avoid raw-spinlocked wakeups from call_rcu_tasks_generic()
  rcu-tasks: Count trylocks to estimate call_rcu_tasks() contention
  rcu-tasks: Add rcupdate.rcu_task_enqueue_lim to set initial queueing
  rcu-tasks: Make rcu_barrier_tasks*() handle multiple callback queues
  rcu-tasks: Use workqueues for multiple rcu_tasks_invoke_cbs() invocations
  rcu-tasks: Abstract invocations of callbacks
  rcu-tasks: Abstract checking of callback lists
  rcu-tasks: Add a ->percpu_enqueue_lim to the rcu_tasks structure
  rcu-tasks: Inspect stalled task's trc state in locked state
  rcu-tasks: Use spin_lock_rcu_node() and friends
  rcutorture: Combine n_max_cbs from all kthreads in a callback flood
  ...
This commit is contained in:
Linus Torvalds
2022-01-11 09:29:44 -08:00
parent a229327733 f80fe66c38
commit e7d38f16c2
68 changed files with 1243 additions and 794 deletions
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68
Documentation/admin-guide/kernel-parameters.txt
View File

@@ -4365,19 +4365,30 @@
Disable the Correctable Errors Collector,
see CONFIG_RAS_CEC help text.
rcu_nocbs= [KNL]
The argument is a cpu list, as described above.
rcu_nocbs[=cpu-list]
[KNL] The optional argument is a cpu list,
as described above.
In kernels built with CONFIG_RCU_NOCB_CPU=y, set
the specified list of CPUs to be no-callback CPUs.
Invocation of these CPUs' RCU callbacks will be
offloaded to "rcuox/N" kthreads created for that
purpose, where "x" is "p" for RCU-preempt, and
"s" for RCU-sched, and "N" is the CPU number.
This reduces OS jitter on the offloaded CPUs,
which can be useful for HPC and real-time
workloads. It can also improve energy efficiency
for asymmetric multiprocessors.
In kernels built with CONFIG_RCU_NOCB_CPU=y,
enable the no-callback CPU mode, which prevents
such CPUs' callbacks from being invoked in
softirq context. Invocation of such CPUs' RCU
callbacks will instead be offloaded to "rcuox/N"
kthreads created for that purpose, where "x" is
"p" for RCU-preempt, "s" for RCU-sched, and "g"
for the kthreads that mediate grace periods; and
"N" is the CPU number. This reduces OS jitter on
the offloaded CPUs, which can be useful for HPC
and real-time workloads. It can also improve
energy efficiency for asymmetric multiprocessors.
If a cpulist is passed as an argument, the specified
list of CPUs is set to no-callback mode from boot.
Otherwise, if the '=' sign and the cpulist
arguments are omitted, no CPU will be set to
no-callback mode from boot but the mode may be
toggled at runtime via cpusets.
rcu_nocb_poll [KNL]
Rather than requiring that offloaded CPUs
@@ -4511,10 +4522,6 @@
on rcutree.qhimark at boot time and to zero to
disable more aggressive help enlistment.
rcutree.rcu_idle_gp_delay= [KNL]
Set wakeup interval for idle CPUs that have
RCU callbacks (RCU_FAST_NO_HZ=y).
rcutree.rcu_kick_kthreads= [KNL]
Cause the grace-period kthread to get an extra
wake_up() if it sleeps three times longer than
@@ -4625,8 +4632,12 @@
in seconds.
rcutorture.fwd_progress= [KNL]
Enable RCU grace-period forward-progress testing
Specifies the number of kthreads to be used
for RCU grace-period forward-progress testing
for the types of RCU supporting this notion.
Defaults to 1 kthread, values less than zero or
greater than the number of CPUs cause the number
of CPUs to be used.
rcutorture.fwd_progress_div= [KNL]
Specify the fraction of a CPU-stall-warning
@@ -4827,6 +4838,29 @@
period to instead use normal non-expedited
grace-period processing.
rcupdate.rcu_task_collapse_lim= [KNL]
Set the maximum number of callbacks present
at the beginning of a grace period that allows
the RCU Tasks flavors to collapse back to using
a single callback queue. This switching only
occurs when rcupdate.rcu_task_enqueue_lim is
set to the default value of -1.
rcupdate.rcu_task_contend_lim= [KNL]
Set the minimum number of callback-queuing-time
lock-contention events per jiffy required to
cause the RCU Tasks flavors to switch to per-CPU
callback queuing. This switching only occurs
when rcupdate.rcu_task_enqueue_lim is set to
the default value of -1.
rcupdate.rcu_task_enqueue_lim= [KNL]
Set the number of callback queues to use for the
RCU Tasks family of RCU flavors. The default
of -1 allows this to be automatically (and
dynamically) adjusted. This parameter is intended
for use in testing.
rcupdate.rcu_task_ipi_delay= [KNL]
Set time in jiffies during which RCU tasks will
avoid sending IPIs, starting with the beginning

2
Documentation/admin-guide/kernel-per-CPU-kthreads.rst
View File

@@ -208,7 +208,7 @@ Do at least one of the following:
2. Enable RCU to do its processing remotely via dyntick-idle by
doing all of the following:
a. Build with CONFIG_NO_HZ=y and CONFIG_RCU_FAST_NO_HZ=y.
a. Build with CONFIG_NO_HZ=y.
b. Ensure that the CPU goes idle frequently, allowing other
CPUs to detect that it has passed through an RCU quiescent
state. If the kernel is built with CONFIG_NO_HZ_FULL=y,