Re: [RFC PATCH 0/2] Introduce serialized smp_call_function APIs
From: Avi Kivity
Date: Wed Mar 13 2024 - 17:58:58 EST
[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.