Re: [PATCH v2] rcuscale: add srcua scale type

[Joel Fernandes <joelagnelf@nvidia.com>]

On 10/3/2026 12:17 PM, Kunwu Chan wrote:
> Add support for scaling atomic SRCU grace periods using
> srcu_read_lock_atomic()/srcu_read_unlock_atomic() and
> synchronize_srcu_atomic().
> 
> Suggested-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Kunwu Chan <kunwu.chan@gmail.com>
> ---
> Changes since v1:
> - Rename srcu_atomic_ctlp to srcua and reuse srcu_ctlp for
>   SRCU operations, as suggested by Paul.
> - Reuse the existing SRCU cleanup and completed helpers by
>   initializing srcu_ctlp in srcu_atomic_scale_init().
> - Add .stats using srcu_scale_stats().
> - Use "srcua" to match the existing "srcu" and "srcud" scale
>   type names.
> - Use synchronize_srcu_atomic() for both normal and expedited
>   scale tests.
> 
> v1: https://lore.kernel.org/all/20260927100359.3903688-1-kunwu.chan@gmail.com/
> Tested with kvm.sh --torture rcuscale scale_type=srcua on x86_64 and
> arm64, alongside gp_exp=1 and PROVE_LOCKING=y: no warnings or lockdep
> splats.
> ---

Maybe some performance numbers too for an rcuscale patch? ;-) But either way:

Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>





>  kernel/rcu/rcuscale.c | 41 ++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
> index 1097ec15879c..b172882824ac 100644
> --- a/kernel/rcu/rcuscale.c
> +++ b/kernel/rcu/rcuscale.c
> @@ -293,6 +293,44 @@ static struct rcu_scale_ops srcud_ops = {
>  	.name		= "srcud"
>  };
>  
> +static struct srcu_struct srcua;
> +
> +static int srcu_scale_atomic_read_lock(void)
> +{
> +	return srcu_read_lock_atomic(srcu_ctlp);
> +}
> +
> +static void srcu_scale_atomic_read_unlock(int idx)
> +{
> +	srcu_read_unlock_atomic(srcu_ctlp, idx);
> +}
> +
> +static void srcu_scale_atomic_synchronize(void)
> +{
> +	synchronize_srcu_atomic(srcu_ctlp);
> +}
> +
> +static void srcu_atomic_scale_init(void)
> +{
> +	srcu_ctlp = &srcua;
> +	init_srcu_struct_atomic(srcu_ctlp);
> +}
> +
> +static struct rcu_scale_ops srcua_ops = {
> +	.ptype		= SRCU_FLAVOR,
> +	.init		= srcu_atomic_scale_init,
> +	.cleanup	= srcu_sync_scale_cleanup,
> +	.readlock	= srcu_scale_atomic_read_lock,
> +	.readunlock	= srcu_scale_atomic_read_unlock,
> +	.get_gp_seq	= srcu_scale_completed,
> +	.gp_diff	= rcu_seq_diff,
> +	.exp_completed	= srcu_scale_completed,
> +	.sync		= srcu_scale_atomic_synchronize,
> +	.exp_sync	= srcu_scale_atomic_synchronize,
> +	.stats		= srcu_scale_stats,
> +	.name		= "srcua"
> +};
> +
>  #ifdef CONFIG_TASKS_RCU
>  
>  /*
> @@ -1110,7 +1148,8 @@ rcu_scale_init(void)
>  	long i;
>  	long j;
>  	static struct rcu_scale_ops *scale_ops[] = {
> -		&rcu_ops, &srcu_ops, &srcud_ops, TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
> +		&rcu_ops, &srcu_ops, &srcua_ops, &srcud_ops,
> +		TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS
>  	};
>  
>  	if (!torture_init_begin(scale_type, verbose))
> 
> base-commit: d21906b0aa1e9573cdb5e7acaca44966b9d1dcd2

-- 
Joel Fernandes