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    Subject[PATCH tip/core/rcu 3/6] doc: Improve rcu_dynticks::dynticks documentation
    Date
    From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

    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>
    ---
    .../RCU/Design/Data-Structures/Data-Structures.html | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
    index f5120a00f511..50be87e59937 100644
    --- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
    +++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
    @@ -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
    --
    2.17.1
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