Date:   Tue, 14 Mar 2023 12:10:16 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Suren Baghdasaryan <surenb@google.com>
Cc:     Domenico Cerasuolo <cerasuolodomenico@gmail.com>,
        linux-kernel@vger.kernel.org, peterz@infradead.org,
        brauner@kernel.org, chris@chrisdown.name
Subject: Re: [PATCH 0/4] sched/psi: Allow unprivileged PSI polling
Message-ID: <20230314161016.GA12250@cmpxchg.org>
References: <20230309170756.52927-1-cerasuolodomenico@gmail.com>
 <CAJuCfpGYrnCoAn+bUdcEZ3OS+5ujDp2iUNXBMRacxNGbJvCY-w@mail.gmail.com>
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On Mon, Mar 13, 2023 at 08:29:37AM -0700, Suren Baghdasaryan wrote:
> On Thu, Mar 9, 2023 at 9:08 AM Domenico Cerasuolo
> <cerasuolodomenico@gmail.com> wrote:
> >
> > PSI offers 2 mechanisms to get information about a specific resource
> > pressure. One is reading from /proc/pressure/<resource>, which gives
> > average pressures aggregated every 2s. The other is creating a pollable
> > fd for a specific resource and cgroup.
> >
> > The trigger creation requires CAP_SYS_RESOURCE, and gives the
> > possibility to pick specific time window and threshold, spawing an RT
> > thread to aggregate the data.
> >
> > Systemd would like to provide containers the option to monitor pressure
> > on their own cgroup and sub-cgroups. For example, if systemd launches a
> > container that itself then launches services, the container should have
> > the ability to poll() for pressure in individual services. But neither
> > the container nor the services are privileged.
> 
> This sounds like an interesting usecase. I'll need to take a closer
> look once I'm back from vacation later this week.
> Thanks!

Thanks, Suren!

There is also the desktop monitoring usecase that Chris Down had
inquired about some while back:

https://lore.kernel.org/all/CAJuCfpGnJBEvQTUeJ_U6+rHmPcMjw_pPL+QFj7Sec5fHZPH67w@mail.gmail.com/T/

The patches should help with that as well.