diff options
Diffstat (limited to 'Documentation/RCU/Design')
7 files changed, 50 insertions, 35 deletions
diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.rst b/Documentation/RCU/Design/Data-Structures/Data-Structures.rst index b34990c7c377..04e16775c752 100644 --- a/Documentation/RCU/Design/Data-Structures/Data-Structures.rst +++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.rst @@ -921,10 +921,10 @@ This portion of the ``rcu_data`` structure is declared as follows: :: - 1 int dynticks_snap; + 1 int watching_snap; 2 unsigned long dynticks_fqs; -The ``->dynticks_snap`` field is used to take a snapshot of the +The ``->watching_snap`` field is used to take a snapshot of the corresponding CPU's dyntick-idle state when forcing quiescent states, and is therefore accessed from other CPUs. Finally, the ``->dynticks_fqs`` field is used to count the number of times this CPU @@ -935,8 +935,8 @@ This portion of the rcu_data structure is declared as follows: :: - 1 long dynticks_nesting; - 2 long dynticks_nmi_nesting; + 1 long nesting; + 2 long nmi_nesting; 3 atomic_t dynticks; 4 bool rcu_need_heavy_qs; 5 bool rcu_urgent_qs; @@ -945,14 +945,14 @@ These fields in the rcu_data structure maintain the per-CPU dyntick-idle state for the corresponding CPU. The fields may be accessed only from the corresponding CPU (and from tracing) unless otherwise stated. -The ``->dynticks_nesting`` field counts the nesting depth of process +The ``->nesting`` field counts the nesting depth of process execution, so that in normal circumstances this counter has value zero or one. NMIs, irqs, and tracers are counted by the -``->dynticks_nmi_nesting`` field. Because NMIs cannot be masked, changes +``->nmi_nesting`` field. Because NMIs cannot be masked, changes to this variable have to be undertaken carefully using an algorithm provided by Andy Lutomirski. The initial transition from idle adds one, and nested transitions add two, so that a nesting level of five is -represented by a ``->dynticks_nmi_nesting`` value of nine. This counter +represented by a ``->nmi_nesting`` value of nine. This counter can therefore be thought of as counting the number of reasons why this CPU cannot be permitted to enter dyntick-idle mode, aside from process-level transitions. @@ -960,12 +960,12 @@ process-level transitions. However, it turns out that when running in non-idle kernel context, the Linux kernel is fully capable of entering interrupt handlers that never exit and perhaps also vice versa. Therefore, whenever the -``->dynticks_nesting`` field is incremented up from zero, the -``->dynticks_nmi_nesting`` field is set to a large positive number, and -whenever the ``->dynticks_nesting`` field is decremented down to zero, -the ``->dynticks_nmi_nesting`` field is set to zero. Assuming that +``->nesting`` field is incremented up from zero, the +``->nmi_nesting`` field is set to a large positive number, and +whenever the ``->nesting`` field is decremented down to zero, +the ``->nmi_nesting`` field is set to zero. Assuming that the number of misnested interrupts is not sufficient to overflow the -counter, this approach corrects the ``->dynticks_nmi_nesting`` field +counter, this approach corrects the ``->nmi_nesting`` field every time the corresponding CPU enters the idle loop from process context. @@ -992,8 +992,8 @@ code. +-----------------------------------------------------------------------+ | **Quick Quiz**: | +-----------------------------------------------------------------------+ -| Why not simply combine the ``->dynticks_nesting`` and | -| ``->dynticks_nmi_nesting`` counters into a single counter that just | +| Why not simply combine the ``->nesting`` and | +| ``->nmi_nesting`` counters into a single counter that just | | counts the number of reasons that the corresponding CPU is non-idle? | +-----------------------------------------------------------------------+ | **Answer**: | diff --git a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst index 5750f125361b..1a5ff1a9f02e 100644 --- a/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst +++ b/Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst @@ -147,11 +147,11 @@ RCU read-side critical sections preceding and following the current idle sojourn. This case is handled by calls to the strongly ordered ``atomic_add_return()`` read-modify-write atomic operation that -is invoked within ``rcu_dynticks_eqs_enter()`` at idle-entry -time and within ``rcu_dynticks_eqs_exit()`` at idle-exit time. -The grace-period kthread invokes ``rcu_dynticks_snap()`` and -``rcu_dynticks_in_eqs_since()`` (both of which invoke -an ``atomic_add_return()`` of zero) to detect idle CPUs. +is invoked within ``ct_kernel_exit_state()`` at idle-entry +time and within ``ct_kernel_enter_state()`` at idle-exit time. +The grace-period kthread invokes first ``ct_rcu_watching_cpu_acquire()`` +(preceded by a full memory barrier) and ``rcu_watching_snap_stopped_since()`` +(both of which rely on acquire semantics) to detect idle CPUs. +-----------------------------------------------------------------------+ | **Quick Quiz**: | diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-dyntick.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-dyntick.svg index 423df00c4df9..3fbc19c48a58 100644 --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-dyntick.svg +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-dyntick.svg @@ -528,7 +528,7 @@ font-style="normal" y="-8652.5312" x="2466.7822" - xml:space="preserve">dyntick_save_progress_counter()</text> + xml:space="preserve">rcu_watching_snap_save()</text> <text style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier" id="text202-7-2-7-2-0" @@ -537,7 +537,7 @@ font-style="normal" y="-8368.1475" x="2463.3262" - xml:space="preserve">rcu_implicit_dynticks_qs()</text> + xml:space="preserve">rcu_watching_snap_recheck()</text> </g> <g id="g4504" @@ -607,7 +607,7 @@ font-weight="bold" font-size="192" id="text202-7-5-3-27-6" - style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_dynticks_eqs_enter()</text> + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">ct_kernel_exit_state()</text> <text xml:space="preserve" x="3745.7725" @@ -638,7 +638,7 @@ font-weight="bold" font-size="192" id="text202-7-5-3-27-6-1" - style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_dynticks_eqs_exit()</text> + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">ct_kernel_enter_state()</text> <text xml:space="preserve" x="3745.7725" diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg index d82a77d03d8c..25c7acc8a4c2 100644 --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp-fqs.svg @@ -844,7 +844,7 @@ font-style="normal" y="1547.8876" x="4417.6396" - xml:space="preserve">dyntick_save_progress_counter()</text> + xml:space="preserve">rcu_watching_snap_save()</text> <g style="fill:none;stroke-width:0.025in" transform="translate(6501.9719,-10685.904)" @@ -899,7 +899,7 @@ font-style="normal" y="1858.8729" x="4414.1836" - xml:space="preserve">rcu_implicit_dynticks_qs()</text> + xml:space="preserve">rcu_watching_snap_recheck()</text> <text xml:space="preserve" x="14659.87" @@ -977,7 +977,7 @@ font-weight="bold" font-size="192" id="text202-7-5-3-27-6" - style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_dynticks_eqs_enter()</text> + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">ct_kernel_exit_state()</text> <text xml:space="preserve" x="3745.7725" @@ -1008,7 +1008,7 @@ font-weight="bold" font-size="192" id="text202-7-5-3-27-6-1" - style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_dynticks_eqs_exit()</text> + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">ct_kernel_enter_state()</text> <text xml:space="preserve" x="3745.7725" diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg index 53e0dc2a2c79..d05bc7b27edb 100644 --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-gp.svg @@ -2974,7 +2974,7 @@ font-style="normal" y="38114.047" x="-334.33856" - xml:space="preserve">dyntick_save_progress_counter()</text> + xml:space="preserve">rcu_watching_snap_save()</text> <g style="fill:none;stroke-width:0.025in" transform="translate(1749.9916,25880.249)" @@ -3029,7 +3029,7 @@ font-style="normal" y="38425.035" x="-337.79462" - xml:space="preserve">rcu_implicit_dynticks_qs()</text> + xml:space="preserve">rcu_watching_snap_recheck()</text> <text xml:space="preserve" x="9907.8887" @@ -3107,7 +3107,7 @@ font-weight="bold" font-size="192" id="text202-7-5-3-27-6" - style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_dynticks_eqs_enter()</text> + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">ct_kernel_exit_state()</text> <text xml:space="preserve" x="3745.7725" @@ -3138,7 +3138,7 @@ font-weight="bold" font-size="192" id="text202-7-5-3-27-6-1" - style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">rcu_dynticks_eqs_exit()</text> + style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier">ct_kernel_enter_state()</text> <text xml:space="preserve" x="3745.7725" diff --git a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg index 4fa7506082bf..a92356ce4011 100644 --- a/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg +++ b/Documentation/RCU/Design/Memory-Ordering/TreeRCU-hotplug.svg @@ -516,7 +516,7 @@ font-style="normal" y="-8652.5312" x="2466.7822" - xml:space="preserve">dyntick_save_progress_counter()</text> + xml:space="preserve">rcu_watching_snap_save()</text> <text style="font-size:192px;font-style:normal;font-weight:bold;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier" id="text202-7-2-7-2-0" @@ -525,7 +525,7 @@ font-style="normal" y="-8368.1475" x="2463.3262" - xml:space="preserve">rcu_implicit_dynticks_qs()</text> + xml:space="preserve">rcu_watching_snap_recheck()</text> <text sodipodi:linespacing="125%" style="font-size:192px;font-style:normal;font-weight:bold;line-height:125%;text-anchor:start;fill:#000000;stroke-width:0.025in;font-family:Courier" diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst index cccafdaa1f84..6125e7068d2c 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -2357,6 +2357,7 @@ section. #. `Sched Flavor (Historical)`_ #. `Sleepable RCU`_ #. `Tasks RCU`_ +#. `Tasks Trace RCU`_ Bottom-Half Flavor (Historical) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -2610,6 +2611,16 @@ critical sections that are delimited by voluntary context switches, that is, calls to schedule(), cond_resched(), and synchronize_rcu_tasks(). In addition, transitions to and from userspace execution also delimit tasks-RCU read-side critical sections. +Idle tasks are ignored by Tasks RCU, and Tasks Rude RCU may be used to +interact with them. + +Note well that involuntary context switches are *not* Tasks-RCU quiescent +states. After all, in preemptible kernels, a task executing code in a +trampoline might be preempted. In this case, the Tasks-RCU grace period +clearly cannot end until that task resumes and its execution leaves that +trampoline. This means, among other things, that cond_resched() does +not provide a Tasks RCU quiescent state. (Instead, use rcu_softirq_qs() +from softirq or rcu_tasks_classic_qs() otherwise.) The tasks-RCU API is quite compact, consisting only of call_rcu_tasks(), synchronize_rcu_tasks(), and @@ -2632,9 +2643,13 @@ moniker. And this operation is considered to be quite rude by real-time workloads that don't want their ``nohz_full`` CPUs receiving IPIs and by battery-powered systems that don't want their idle CPUs to be awakened. +Once kernel entry/exit and deep-idle functions have been properly tagged +``noinstr``, Tasks RCU can start paying attention to idle tasks (except +those that are idle from RCU's perspective) and then Tasks Rude RCU can +be removed from the kernel. + The tasks-rude-RCU API is also reader-marking-free and thus quite compact, -consisting of call_rcu_tasks_rude(), synchronize_rcu_tasks_rude(), -and rcu_barrier_tasks_rude(). +consisting solely of synchronize_rcu_tasks_rude(). Tasks Trace RCU ~~~~~~~~~~~~~~~ |
