Re: [PATCH] docs: accounting/psi: drop stale 500ms window minimum from trigger docs

[Suren Baghdasaryan]

On Thu, Jul 23, 2026 at 5:51 AM Tao Cui <cui.tao@xxxxxxxxx> wrote:
>
> From: Tao Cui <cuitao@xxxxxxxxxx>
>
> psi.rst says trigger windows range "from 500ms to 10s" with a 50ms min
> polling interval. That minimum was removed in commit 519fabc7aaba ("psi:
> remove 500ms min window size limitation for triggers"): the polling-rate
> protection moved to gating trigger creation behind CAP_SYS_RESOURCE,
> which also stopped capping psi event latency.
>
> Update the wording accordingly: windows up to 10s with no enforced
> minimum; trigger creation requires CAP_SYS_RESOURCE on cgroup pressure
> files, while unprivileged users on /proc/pressure/ are limited to 2s
> multiples.
>
> Signed-off-by: Tao Cui <cuitao@xxxxxxxxxx>
> ---
>  Documentation/accounting/psi.rst | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/accounting/psi.rst b/Documentation/accounting/psi.rst
> index d455db3e5808..aae57fb5f15c 100644
> --- a/Documentation/accounting/psi.rst
> +++ b/Documentation/accounting/psi.rst
> @@ -99,15 +99,14 @@ psi metric and deactivates upon exit from the stall state. While system is
>  in the stall state psi signal growth is monitored at a rate of 10 times per
>  tracking window.
>
> -The kernel accepts window sizes ranging from 500ms to 10s, therefore min
> -monitoring update interval is 50ms and max is 1s. Min limit is set to
> -prevent overly frequent polling. Max limit is chosen as a high enough number
> -after which monitors are most likely not needed and psi averages can be used
> -instead.
> -
> -Unprivileged users can also create monitors, with the only limitation that the
> -window size must be a multiple of 2s, in order to prevent excessive resource
> -usage.
> +The kernel accepts window sizes up to 10s. The 10s maximum is chosen as a
> +high enough number after which monitors are most likely not needed and psi
> +averages can be used instead.
> +
> +To prevent excessive resource usage, trigger creation is restricted to
> +privileged users (CAP_SYS_RESOURCE) on cgroup pressure files; on the
> +system-wide /proc/pressure/ files unprivileged users can create monitors
> +as well, limited to window sizes that are a multiple of 2s.

Hmm. From this wording it sounds like we have different trigger
creation rules for system-wide vs cgroup pressure files, which I think
is not true. AFAICT, for both types, we restrict unprivileged users to
creating triggers with 2s window size multiples.

>
>  When activated, psi monitor stays active for at least the duration of one
>  tracking window to avoid repeated activations/deactivations when system is
> --
> 2.43.0
>