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doc: Improve rcu_dynticks::dynticks documentation 

The very useful RCU Data-Structures describes that the dynticks counter
of the rcu_dynticks data structure is incremented when we transitions to
or from dynticks-idle mode. However it doesn't mention that it is also
incremented due to transitions to and from user mode which for dynticks
purposes is an extended quiescent state.

I found this with tracing calls to rcu_dynticks_eqs_enter which can also
happen from rcu_user_enter. Lets add this information to the
Data-Structures document.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Joel Fernandes (Google) 2018-06-24 12:34:51 -07:00 committed by Paul E. McKenney
parent a5a2889544
commit ea24c125fe
1 changed files with 5 additions and 3 deletions
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8
Documentation/RCU/Design/Data-Structures/Data-Structures.html
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@ -1227,9 +1227,11 @@ to overflow the counter, this approach corrects the
CPU enters the idle loop from process context.
</p><p>The <tt>-&gt;dynticks</tt> field counts the corresponding
CPU's transitions to and from dyntick-idle mode, so that this counter
has an even value when the CPU is in dyntick-idle mode and an odd
value otherwise.
CPU's transitions to and from either dyntick-idle or user mode, so
that this counter has an even value when the CPU is in dyntick-idle
mode or user mode and an odd value otherwise. The transitions to/from
user mode need to be counted for user mode adaptive-ticks support
(see timers/NO_HZ.txt).
</p><p>The <tt>-&gt;rcu_need_heavy_qs</tt> field is used
to record the fact that the RCU core code would really like to