From c9b6f899e120c83ef144b3d4a8365413ef49cce4 Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Wed, 3 Oct 2018 17:37:25 -0700 Subject: [PATCH] doc: Remove rcu_dynticks from Data-Structures rcu_dynticks was folded into rcu_data structure. Update the data structures RCU document accordingly. Signed-off-by: Joel Fernandes (Google) Cc: Signed-off-by: Paul E. McKenney --- .../BigTreeClassicRCUBHdyntick.svg | 695 ------------------ .../Data-Structures/Data-Structures.html | 90 +-- 2 files changed, 25 insertions(+), 760 deletions(-) delete mode 100644 Documentation/RCU/Design/Data-Structures/BigTreeClassicRCUBHdyntick.svg diff --git a/Documentation/RCU/Design/Data-Structures/BigTreeClassicRCUBHdyntick.svg b/Documentation/RCU/Design/Data-Structures/BigTreeClassicRCUBHdyntick.svg deleted file mode 100644 index 21ba7823479d..000000000000 --- a/Documentation/RCU/Design/Data-Structures/BigTreeClassicRCUBHdyntick.svg +++ /dev/null @@ -1,695 +0,0 @@ - - - - - - - - - - - - image/svg+xml - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - rcu_bh - - struct - - rcu_node - - struct - - rcu_node - - rcu_node - - struct - - struct - - rcu_data - - struct - - rcu_data - - struct - - rcu_data - - struct - - rcu_data - - struct rcu_state - - struct - - rcu_dynticks - - struct - - rcu_dynticks - - struct - - rcu_dynticks - - struct - - rcu_dynticks - - rcu_sched - - - - - diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html index 476b1ac38e4c..4eb603e3a005 100644 --- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html +++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html @@ -23,8 +23,6 @@ to each other. The rcu_segcblist Structure
  • The rcu_data Structure -
  • - The rcu_dynticks Structure
  • The rcu_head Structure
  • @@ -174,16 +172,8 @@ said to be in dyntick-idle mode. RCU must handle dyntick-idle CPUs specially because RCU would otherwise wake up each CPU on every grace period, which would defeat the whole purpose of CONFIG_NO_HZ_IDLE. -RCU uses the rcu_dynticks structure to track -which CPUs are in dyntick idle mode, as shown below: - -

    BigTreeClassicRCUBHdyntick.svg - -

    However, if a CPU is in dyntick-idle mode, it is in that mode -for all flavors of RCU. -Therefore, a single rcu_dynticks structure is allocated per -CPU, and all of a given CPU's rcu_data structures share -that rcu_dynticks, as shown in the figure. +RCU uses the dynticks related fields in the rcu_data structure +to track which CPUs are in dyntick idle mode.

    Kernels built with CONFIG_PREEMPT_RCU support rcu_preempt in addition to rcu_sched and rcu_bh, as shown below: @@ -216,9 +206,6 @@ its own synchronization:

  • Each rcu_node structure has a spinlock.
  • The fields in rcu_data are private to the corresponding CPU, although a few can be read and written by other CPUs. -
  • Similarly, the fields in rcu_dynticks are private - to the corresponding CPU, although a few can be read by - other CPUs.

    It is important to note that different data structures can have @@ -274,11 +261,6 @@ follows: access to this information from the corresponding CPU. Finally, this structure records past dyntick-idle state for the corresponding CPU and also tracks statistics. -

  • rcu_dynticks: - This per-CPU structure tracks the current dyntick-idle - state for the corresponding CPU. - Unlike the other three structures, the rcu_dynticks - structure is not replicated per RCU flavor.
  • rcu_head: This structure represents RCU callbacks, and is the only structure allocated and managed by RCU users. @@ -289,8 +271,8 @@ follows:

    If all you wanted from this article was a general notion of how RCU's data structures are related, you are done. Otherwise, each of the following sections give more details on -the rcu_state, rcu_node, rcu_data, -and rcu_dynticks data structures. +the rcu_state, rcu_node and rcu_data data +structures.

    The rcu_state Structure

    @@ -1017,30 +999,19 @@ as follows: 
       1   int cpu;
-  2   struct rcu_state *rsp;
-  3   struct rcu_node *mynode;
-  4   struct rcu_dynticks *dynticks;
-  5   unsigned long grpmask;
-  6   bool beenonline;
+  2   struct rcu_node *mynode;
+  3   unsigned long grpmask;
+  4   bool beenonline;

    The ->cpu field contains the number of the -corresponding CPU, the ->rsp pointer references -the corresponding rcu_state structure (and is most frequently -used to locate the name of the corresponding flavor of RCU for tracing), -and the ->mynode field references the corresponding -rcu_node structure. +corresponding CPU and the ->mynode field references the +corresponding rcu_node structure. The ->mynode is used to propagate quiescent states up the combining tree. -

    The ->dynticks pointer references the -rcu_dynticks structure corresponding to this -CPU. -Recall that a single per-CPU instance of the rcu_dynticks -structure is shared among all flavors of RCU. -These first four fields are constant and therefore require not -synchronization. +These two fields are constant and therefore do not require synchronization. -

    The ->grpmask field indicates the bit in +

    The ->grpmask field indicates the bit in the ->mynode->qsmask corresponding to this rcu_data structure, and is also used when propagating quiescent states. @@ -1181,26 +1152,22 @@ Finally, the ->dynticks_fqs field is used to count the number of times this CPU is determined to be in dyntick-idle state, and is used for tracing and debugging purposes. -

    -The rcu_dynticks Structure

    - -

    The rcu_dynticks maintains the per-CPU dyntick-idle state -for the corresponding CPU. -Unlike the other structures, rcu_dynticks is not -replicated over the different flavors of RCU. -The fields in this structure may be accessed only from the corresponding -CPU (and from tracing) unless otherwise stated. -Its fields are as follows: +

    +This portion of the rcu_data structure is declared as follows: 

       1   long dynticks_nesting;
   2   long dynticks_nmi_nesting;
   3   atomic_t dynticks;
   4   bool rcu_need_heavy_qs;
-  5   unsigned long rcu_qs_ctr;
-  6   bool rcu_urgent_qs;
+  5   bool rcu_urgent_qs;
    +

    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 execution, so that in normal circumstances this counter has value zero or one. @@ -1242,19 +1209,12 @@ it is willing to call for heavy-weight dyntick-counter operations. This flag is checked by RCU's context-switch and cond_resched() code, which provide a momentary idle sojourn in response. -

    The ->rcu_qs_ctr field is used to record -quiescent states from cond_resched(). -Because cond_resched() can execute quite frequently, this -must be quite lightweight, as in a non-atomic increment of this -per-CPU field. -

    Finally, the ->rcu_urgent_qs field is used to record -the fact that the RCU core code would really like to see a quiescent -state from the corresponding CPU, with the various other fields indicating -just how badly RCU wants this quiescent state. -This flag is checked by RCU's context-switch and cond_resched() -code, which, if nothing else, non-atomically increment ->rcu_qs_ctr -in response. +the fact that the RCU core code would really like to see a quiescent state from +the corresponding CPU, with the various other fields indicating just how badly +RCU wants this quiescent state. +This flag is checked by RCU's context-switch path +(rcu_note_context_switch) and the cond_resched code. @@ -1431,7 +1391,7 @@ So each flavor of RCU is represented by an rcu_state structure, which contains a combining tree of rcu_node and rcu_data structures. Finally, in CONFIG_NO_HZ_IDLE kernels, each CPU's dyntick-idle -state is tracked by an rcu_dynticks structure. +state is tracked by dynticks-related fields in the rcu_data structure. If you made it this far, you are well prepared to read the code walkthroughs in the other articles in this series.