diff options
| author | Domenico Cerasuolo <cerasuolodomenico@gmail.com> | 2023-03-30 12:54:18 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-04-05 09:58:50 +0200 |
| commit | d82caa273565b45fcf103148950549af76c314b0 (patch) | |
| tree | 8a323eb619bf814129fe584ef7984bfac3d4a01c /Documentation/accounting | |
| parent | 4468fcae49f08e88fbbffe05b29496192df89991 (diff) | |
sched/psi: Allow unprivileged polling of N*2s period
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 patch implements a mechanism to allow unprivileged users to create
pressure triggers. The difference with privileged triggers creation is
that unprivileged ones must have a time window that's a multiple of 2s.
This is so that we can avoid unrestricted spawning of rt threads, and
use instead the same aggregation mechanism done for the averages, which
runs independently of any triggers.
Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lore.kernel.org/r/20230330105418.77061-5-cerasuolodomenico@gmail.com
Diffstat (limited to 'Documentation/accounting')
| -rw-r--r-- | Documentation/accounting/psi.rst | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/Documentation/accounting/psi.rst b/Documentation/accounting/psi.rst index 5e40b3f437f9..df6062eb3abb 100644 --- a/Documentation/accounting/psi.rst +++ b/Documentation/accounting/psi.rst @@ -105,6 +105,10 @@ 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. + When activated, psi monitor stays active for at least the duration of one tracking window to avoid repeated activations/deactivations when system is bouncing in and out of the stall state. |