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SubjectRe: [PATCH 0/2] bind rcu offload (nohz_full/isolation) into cpuset
On Wed, Oct 27, 2021 at 04:43:17PM -0400, Paul Gortmaker wrote:
> One of the earlier pre-mainline RCU nocb patchsets had a temporary sysfs
> knob in /sys/devices/system/cpu/cpu*/hotplug/nocb for testing[1].
>
> That not-for-merge commit from Frederic said:
>
> This is only intended for those who want to test this patchset. The
> real interfaces will be cpuset/isolation and rcutorture.
>
> We've had rcutorture as the one and only mainline user of nocb toggle
> for a while now[2], and so I thought I'd take a crack at what Frederic
> had in mind for cpuset with some code vs. asking 100 random questions.
>
> Note that I intentionally didn't Cc any cgroup/cpuset people (yet),
> since at this point this is only my guess on what things were to look
> like based on a single sentence fragment. So this is really early
> "Not-for-Merge", but truly just RFC -- to start a conversation.
>
> It won't be really useful until we adjust tick/housekeeping in addition
> to nocb, but I think we can develop the interface in parallel to that?
> And maybe use this to expand testing at the same time if it is layered
> on top of those future work/patchsets? I don't know...
>
> We'll also have to look at corner cases - like whether we want to treat
> the root cpuset differently; whether we want to sync boot arg values
> with the cpuset's initial isol flag value, whether we un-isolate cores
> when an isolation cpuset is rmdir/removed, etc etc.
>
> But as a proof of concept, it "works" as can be seen in the 2nd commit.

I'm working on the same thing :o)

With quite a rework of housekeeping core behind (WIP):

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
isolation/split

It's not yet ready either and I'm glad you posted this, it shows I'm not
the only one interested in it.

One thing about cpuset: I arranged to implement it only on cgroup v2 and
exclusively mutable on root partition (which doesn't mean only _the_ root
partition but also those whose cpuset.cpus.partition == "root". This way
I make sure the set of cpus is exclusive. I didn't want to bother with
intersecting cpusets with different nocb values.

Thanks.

> Paul.
> --
>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Frederic Weisbecker <frederic@kernel.org>
> Cc: Valentin Schneider <valentin.schneider@arm.com>
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git/commit/?h=rcu/nocb&id=6abe8408307e
> part of https://lwn.net/Articles/820544/
> https://lwn.net/Articles/832031/ <------ v2
> https://lwn.net/Articles/835039/ <------ v3
> https://lwn.net/Articles/837128/ <------ v4
>
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d97b078182406
>
>
> Paul Gortmaker (2):
> sched: isolation: cpu isolation handles for cpuset
> cpuset: add binding to CPU isolation
>
> include/linux/sched/isolation.h | 4 ++++
> kernel/cgroup/cpuset.c | 42 +++++++++++++++++++++++++++++++++++++++++
> kernel/sched/isolation.c | 22 +++++++++++++++++++++
> 3 files changed, 68 insertions(+)
>
> --
> 2.15.0
>

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