linux-kernel - [PATCH 0/2] sched: issues with sched_rt_runtime

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Message-ID: <20250306052954.452005-1-sshegde@linux.ibm.com>
Date: Thu,  6 Mar 2025 10:59:52 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: juri.lelli@...hat.com, linux-kernel@...r.kernel.org
Cc: sshegde@...ux.ibm.com, mingo@...nel.org, peterz@...radead.org,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        vschneid@...hat.com, hbathini@...ux.ibm.com, joelagnelf@...dia.com
Subject: [PATCH 0/2] sched: issues with sched_rt_runtime_us

ftrace selftest reported below failure in one of the systems.
[5] Test tracefs GID mount option       [FAIL]

On inspection this happens since writing -1 to sched_rt_runtime_us 
fails. This happened because the possible cpus were more than the 
active cpus. 

Fix this issue by considering only the online CPUs for validating the 
deadline entities. This is minimal impact compared to changing the 
dl_bw_cpus use possible mask. If that is better, we can follow that
approach. 

There is also another issue that is observed when working on it. Writing
any value less than 5% of period results in -EBUSY. This happens since 
fair_server dl_server allocates 5% of the bandwidth and that is part of
the bandwidth of the root domain. Lets document that behaviour since
the file allows writing -1 as the minimum. 

Shrikanth Hegde (2):
  sched/deadline: use online cpus for validating runtime
  sched/rt: update limit of sched_rt sysctl in documentation

 Documentation/scheduler/sched-rt-group.rst | 3 +++
 kernel/sched/deadline.c                    | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

-- 
2.39.3