Re: [RFC PATCH 0/2] Introduce serialized smp_call_function APIs

[Avi Kivity]

[resend in plain text for the list]

On Wed, 2024-03-13 at 16:56 -0400, Mathieu Desnoyers wrote:
> commit 944d5fe50f3f ("sched/membarrier: reduce the ability to hammer
> on sys_membarrier")
> introduces a mutex over all membarrier operations to reduce its
> ability
> to slow down the rest of the system.
> 
> This RFC series has two objectives:
> 
> 1) Move this mutex to the smp_call_function APIs so other system
> calls
>    using smp_call_function IPIs are limited in the same way,
> 
> 2) Restore scalability of MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ with
>    MEMBARRIER_CMD_FLAG_CPU, which targets specific CPUs with IPIs.
>    This may or may not be useful, and I would welcome benchmarks from
>    users of this feature to figure out if this is worth it.
> 

I see this doesn't restore scaling of MEMBARRIER_CMD_PRIVATE_EXPEDITED,
which I use (and wasn't aware was broken).

I don't have comments on the patches, but do have ideas on how to work
around the problem in Seastar. So this was a useful heads-up for me.