Re: [PATCH] cpuhp: Expedite synchronize_rcu during SMT switch

[Joel Fernandes]

On Sun, Jan 19, 2026 at 03:11:18PM +0100, Peter Zijlstra wrote:
> By holding an extra rcu_sync reference, the percpu rwsem is kept into
> the the slow path, avoiding the rcu-sync on down_write(), which was very
> prevalent per this:
>
>   https://lkml.kernel.org/r/aWU9HRcs4ghazIRg@xxxxxxxxxxxxx

Makes sense, though I wonder if we should have a separate percpu-rwsem API
for this rather than directly accessing the lock-internal rcu_sync state?
Other future percpu_rw_semaphore users may benefit as well.

 - Joel