Re: [PATCH v7 4/5] locking/qspinlock: Introduce starvation avoidance into CNA

[Waiman Long <longman@redhat.com>]

On 11/25/19 4:07 PM, Alex Kogan wrote:
> Keep track of the number of intra-node lock handoffs, and force
> inter-node handoff once this number reaches a preset threshold.
> The default value for the threshold can be overridden with
> the new kernel boot command-line option "numa_spinlock_threshold".
>
> Signed-off-by: Alex Kogan <alex.kogan@oracle.com>
> Reviewed-by: Steve Sistare <steven.sistare@oracle.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |  8 ++++++
>  arch/x86/kernel/alternative.c                 | 27 +++++++++++++++++++
>  kernel/locking/qspinlock.c                    |  3 +++
>  kernel/locking/qspinlock_cna.h                | 27 ++++++++++++++++---
>  4 files changed, 62 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 904cb32f592d..887fbfce701d 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3185,6 +3185,14 @@
>  			Not specifying this option is equivalent to
>  			numa_spinlock=auto.
>  
> +	numa_spinlock_threshold=	[NUMA, PV_OPS]
> +			Set the threshold for the number of intra-node
> +			lock hand-offs before the NUMA-aware spinlock
> +			is forced to be passed to a thread on another NUMA node.
> +			Valid values are in the [0..31] range. Smaller values
> +			result in a more fair, but less performant spinlock, and
> +			vice versa. The default value is 16.
> +
>  	cpu0_hotplug	[X86] Turn on CPU0 hotplug feature when
>  			CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
>  			Some features depend on CPU0. Known dependencies are:
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 6a4ccbf4e09c..28552e0491b5 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -723,6 +723,33 @@ static int __init numa_spinlock_setup(char *str)
>  
>  __setup("numa_spinlock=", numa_spinlock_setup);
>  
> +/*
> + * Controls the threshold for the number of intra-node lock hand-offs before
> + * the NUMA-aware variant of spinlock is forced to be passed to a thread on
> + * another NUMA node. By default, the chosen value provides reasonable
> + * long-term fairness without sacrificing performance compared to a lock
> + * that does not have any fairness guarantees.
> + */
> +int intra_node_handoff_threshold = 1 << 16;

      ^
      __ro_after_init

> +
> +static int __init numa_spinlock_threshold_setup(char *str)
> +{
> +	int new_threshold_param;
> +
> +	if (get_option(&str, &new_threshold_param)) {
> +		/* valid value is between 0 and 31 */
> +		if (new_threshold_param < 0 || new_threshold_param > 31)
> +			return 0;
> +
> +		intra_node_handoff_threshold = 1 << new_threshold_param;
> +		return 1;
> +	}
> +
> +	return 0;
> +}
> +
> +__setup("numa_spinlock_threshold=", numa_spinlock_threshold_setup);
> +
>  #endif
>  

Against, this should be in qspinlock_can.h not in alternative.c.

Cheers,
Longman