Re: [PATCH 02/27] sched/isolation: Introduce housekeeping per-cpu rwsem

[Tejun Heo]

Hello,

On Mon, Jun 23, 2025 at 01:57:17PM -0400, Waiman Long wrote:
> The percpu-rwsem does have a cheaper read side compared with rwsem for
> typical use case where writer update happens sparingly. However, when the
> writer has successful acquired the write lock, the readers do have to wait
> until the writer issues a percpu_up_write() call before they can proceed. It
> is the delay introduced by this wait that I am worry about. Isolated
> partitions are typically set up to run RT applications that have a strict
> latency requirement. So any possible latency spike should be avoided.

I see. Hmm... this being the mechanism that establishes the isolation, it
doesn't seem too broken if things stutter a bit when isolation is being
updated. Let's see what Frederic says why the strong interlocking is needed.

Thanks.

-- 
tejun