On Mon, Jul 15, 2024 at 04:23:24PM -0700, JP Kobryn wrote:
> Using a higher value for the initial gp sequence counters allows for
> wrapping to occur faster. It can help with surfacing any issues that may
> be happening as a result of the wrap around.
>
> Signed-off-by: JP Kobryn <inwardvessel@xxxxxxxxx>
Much nicer, thank you!
Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> ---
> kernel/rcu/srcutree.c | 10 +++++++---
> 1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> index bc4b58b0204e..907c4a484503 100644
> --- a/kernel/rcu/srcutree.c
> +++ b/kernel/rcu/srcutree.c
> @@ -30,6 +30,9 @@
> #include "rcu.h"
> #include "rcu_segcblist.h"
>
> +/* Start with a gp sequence value that allows wrapping to occur faster. */
> +#define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT)
> +
> /* Holdoff in nanoseconds for auto-expediting. */
> #define DEFAULT_SRCU_EXP_HOLDOFF (25 * 1000)
> static ulong exp_holdoff = DEFAULT_SRCU_EXP_HOLDOFF;
> @@ -247,7 +250,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
> mutex_init(&ssp->srcu_sup->srcu_cb_mutex);
> mutex_init(&ssp->srcu_sup->srcu_gp_mutex);
> ssp->srcu_idx = 0;
> - ssp->srcu_sup->srcu_gp_seq = 0;
> + ssp->srcu_sup->srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL;
> ssp->srcu_sup->srcu_barrier_seq = 0;
> mutex_init(&ssp->srcu_sup->srcu_barrier_mutex);
> atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0);
> @@ -258,7 +261,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
> if (!ssp->sda)
> goto err_free_sup;
> init_srcu_struct_data(ssp);
> - ssp->srcu_sup->srcu_gp_seq_needed_exp = 0;
> + ssp->srcu_sup->srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL;
> ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns();
> if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) {
> if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC))
> @@ -266,7 +269,8 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static)
> WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG);
> }
> ssp->srcu_sup->srcu_ssp = ssp;
> - smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed, 0); /* Init done. */
> + smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed,
> + SRCU_GP_SEQ_INITIAL_VAL); /* Init done. */
> return 0;
>
> err_free_sda:
> --
> 2.45.2
>
