Re: [PATCH v2 tip/core/rcu 6/6] srcu: Document polling interfaces for Tree SRCU grace periods

Neeraj Upadhyay
2020-11-27T08:27:44Z

On 11/21/2020 6:29 AM, paulmck@kernel.org wrote:
> From: "Paul E. McKenney" <paulmck@kernel.org>
>
> This commit adds requirements documentation for the
> get_state_synchronize_srcu(), start_poll_synchronize_srcu(), and
> poll_state_synchronize_srcu() functions.
>
> Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
> Reported-by: Kent Overstreet <kent.overstreet@gmail.com>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> ---

Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>

Thanks
Neeraj

> Documentation/RCU/Design/Requirements/Requirements.rst | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
> index 1e3df77..2dce79d 100644
> --- a/Documentation/RCU/Design/Requirements/Requirements.rst
> +++ b/Documentation/RCU/Design/Requirements/Requirements.rst
> @@ -2600,6 +2600,24 @@ also includes DEFINE_SRCU(), DEFINE_STATIC_SRCU(), and
> init_srcu_struct() APIs for defining and initializing
> ``srcu_struct`` structures.
>
> +More recently, the SRCU API has added polling interfaces:
> +
> +#. start_poll_synchronize_srcu() returns a cookie identifying
> + the completion of a future SRCU grace period and ensures
> + that this grace period will be started.
> +#. poll_state_synchronize_srcu() returns ``true`` iff the
> + specified cookie corresponds to an already-completed
> + SRCU grace period.
> +#. get_state_synchronize_srcu() returns a cookie just like
> + start_poll_synchronize_srcu() does, but differs in that
> + it does nothing to ensure that any future SRCU grace period
> + will be started.
> +
> +These functions are used to avoid unnecessary SRCU grace periods in
> +certain types of buffer-cache algorithms having multi-stage age-out
> +mechanisms. The idea is that by the time the block has aged completely
> +from the cache, an SRCU grace period will be very likely to have elapsed.
> +
> Tasks RCU
> ~~~~~~~~~
>
>

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