linux-kernel - Re: [PATCH v2 20/23] sched: psi: implement bpf

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Message-ID: <aQD_-a8oWHfRKcrX@slm.duckdns.org>
Date: Tue, 28 Oct 2025 07:40:09 -1000
From: Tejun Heo <tj@...nel.org>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	Alexei Starovoitov <ast@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...nel.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	JP Kobryn <inwardvessel@...il.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, bpf@...r.kernel.org,
	Martin KaFai Lau <martin.lau@...nel.org>,
	Song Liu <song@...nel.org>,
	Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH v2 20/23] sched: psi: implement bpf_psi struct ops

Hello,

On Mon, Oct 27, 2025 at 04:22:03PM -0700, Roman Gushchin wrote:
> This patch implements a BPF struct ops-based mechanism to create
> PSI triggers, attach them to cgroups or system wide and handle
> PSI events in BPF.
> 
> The struct ops provides 3 callbacks:
>   - init() called once at load, handy for creating PSI triggers
>   - handle_psi_event() called every time a PSI trigger fires
>   - handle_cgroup_online() called when a new cgroup is created
>   - handle_cgroup_offline() called if a cgroup with an attached
>     trigger is deleted
> 
> A single struct ops can create a number of PSI triggers, both
> cgroup-scoped and system-wide.
> 
> All 4 struct ops callbacks can be sleepable. handle_psi_event()
> handlers are executed using a separate workqueue, so it won't
> affect the latency of other PSI triggers.

Here, too, I wonder whether it's necessary to build a hard-coded
infrastructure to hook into PSI's triggers. psi_avgs_work() is what triggers
these events and it's not that hot. Wouldn't a fexit attachment to that
function that reads the updated values be enough? We can also easily add a
TP there if a more structured access is desirable.

Thanks.

-- 
tejun