Re: [RFC PATCH 0/8] cgroup/cpuset: Support RCU_NOCB on isolated partitions

From: Waiman Long
Date: Sat Feb 10 2024 - 20:47:00 EST

On 1/19/24 05:24, Paul E. McKenney wrote:
On Wed, Jan 17, 2024 at 11:35:03AM -0500, Waiman Long wrote:
This patch series is based on the RFC patch from Frederic [1]. Instead
of offering RCU_NOCB as a separate option, it is now lumped into a
root-only cpuset.cpus.isolation_full flag that will enable all the
additional CPU isolation capabilities available for isolated partitions
if set. RCU_NOCB is just the first one to this party. Additional dynamic
CPU isolation capabilities will be added in the future.

The first 2 patches are adopted from Federic with minor twists to fix
merge conflicts and compilation issue. The rests are for implementing
the new cpuset.cpus.isolation_full interface which is essentially a flag
to globally enable or disable full CPU isolation on isolated partitions.
On read, it also shows the CPU isolation capabilities that are currently
enabled. RCU_NOCB requires that the rcu_nocbs option be present in
the kernel boot command line. Without that, the rcu_nocb functionality
cannot be enabled even if the isolation_full flag is set. So we allow
users to check the isolation_full file to verify that if the desired
CPU isolation capability is enabled or not.

Only sanity checking has been done so far. More testing, especially on
the RCU side, will be needed.
There has been some discussion of simplifying the (de-)offloading code
to handle only offline CPUs. Along with some discussion of eliminating
the (de-)offloading capability altogehter.

We clearly should converge on the capability to be provided before
exposing this to userspace. ;-)

Would you mind giving me a pointer to the discussion of simplifying the de-offloading code to  handle only offline CPUs?