Re: [PATCH 1/2] membarrier: allow cpu_id to be set on more commands

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

On 2025-06-26 11:52, Dylan Yudaken wrote:
> No reason to not allow MEMBARRIER_CMD_FLAG_CPU on
> MEMBARRIER_CMD_PRIVATE_EXPEDITED or
> MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE.
> 
> If it is known specifically what cpu you want to interrupt then there
> is a decent efficiency saving in not interrupting all the other ones.
> 
> Also - the code already works as is for them.

Can you elaborate on a concrete use-case justifying adding this ?

Thanks,

Mathieu

> 
> Signed-off-by: Dylan Yudaken <dyudaken@gmail.com>
> ---
>   kernel/sched/membarrier.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
> index 809194cd779f..def6d4094ad6 100644
> --- a/kernel/sched/membarrier.c
> +++ b/kernel/sched/membarrier.c
> @@ -595,7 +595,9 @@ static int membarrier_get_registrations(void)
>    *          contains the CPU on which to interrupt (= restart)
>    *          the RSEQ critical section.
>    * @cpu_id: if @flags == MEMBARRIER_CMD_FLAG_CPU, indicates the cpu on which
> - *          RSEQ CS should be interrupted (@cmd must be
> + *          RSEQ CS should be interrupted (@cmd must be one of
> + *          MEMBARRIER_CMD_PRIVATE_EXPEDITED,
> + *          MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE,
>    *          MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ).
>    *
>    * If this system call is not implemented, -ENOSYS is returned. If the
> @@ -625,6 +627,8 @@ static int membarrier_get_registrations(void)
>   SYSCALL_DEFINE3(membarrier, int, cmd, unsigned int, flags, int, cpu_id)
>   {
>   	switch (cmd) {
> +	case MEMBARRIER_CMD_PRIVATE_EXPEDITED:
> +	case MEMBARRIER_CMD_PRIVATE_EXPEDITED_SYNC_CORE:
>   	case MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ:
>   		if (unlikely(flags && flags != MEMBARRIER_CMD_FLAG_CPU))
>   			return -EINVAL;


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com