This series introduces a new sysctl_sched_uclamp_util_min_rt_default to control at runtime the default boost value of RT tasks. Full rationale is in patch 1 commit message. v6 has changed the approach taken in v5 [1] and earlier by moving away from the lazy update approach that touched the fast path to a synchronous one that is performed when the write to the procfs entry is done. for_each_process_thread() is used to update all existing RT tasks now. And to handle the race with a concurrent fork() we introduce sched_post_fork() in _do_fork() to ensure a concurrently forked RT tasks gets the right update. To ensure the race condition is handled correctly, I wrote this small (simple!) test program: https://github.com/qais-yousef/uclamp_test.git And ran it on 4core x86 system and 8core big.LITTLE juno-r2 system. >From juno-r2 run, 10 iterations each run: Without sched_post_fork() # ./run.sh pid 3105 has 336 but default should be 337 pid 13162 has 336 but default should be 337 pid 23256 has 338 but default should be 339 All forked RT tasks had the correct uclamp.min pid 10638 has 334 but default should be 335 All forked RT tasks had the correct uclamp.min pid 30683 has 335 but default should be 336 pid 8247 has 336 but default should be 337 pid 18170 has 1024 but default should be 334 pid 28274 has 336 but default should be 337 With sched_post_fork() # ./run.sh All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min All forked RT tasks had the correct uclamp.min Thanks -- Qais Yousef [1] https://lore.kernel.org/lkml/20200511154053.7822-1-qais.yousef@xxxxxxx/ CC: Jonathan Corbet <corbet@xxxxxxx> CC: Juri Lelli <juri.lelli@xxxxxxxxxx> CC: Vincent Guittot <vincent.guittot@xxxxxxxxxx> CC: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> CC: Steven Rostedt <rostedt@xxxxxxxxxxx> CC: Ben Segall <bsegall@xxxxxxxxxx> CC: Mel Gorman <mgorman@xxxxxxx> CC: Luis Chamberlain <mcgrof@xxxxxxxxxx> CC: Kees Cook <keescook@xxxxxxxxxxxx> CC: Iurii Zaikin <yzaikin@xxxxxxxxxx> CC: Quentin Perret <qperret@xxxxxxxxxx> CC: Valentin Schneider <valentin.schneider@xxxxxxx> CC: Patrick Bellasi <patrick.bellasi@xxxxxxxxxx> CC: Pavan Kondeti <pkondeti@xxxxxxxxxxxxxx> CC: linux-doc@xxxxxxxxxxxxxxx CC: linux-kernel@xxxxxxxxxxxxxxx CC: linux-fsdevel@xxxxxxxxxxxxxxx Qais Yousef (2): sched/uclamp: Add a new sysctl to control RT default boost value Documentation/sysctl: Document uclamp sysctl knobs Documentation/admin-guide/sysctl/kernel.rst | 54 ++++++++ include/linux/sched/sysctl.h | 1 + include/linux/sched/task.h | 1 + kernel/fork.c | 1 + kernel/sched/core.c | 132 ++++++++++++++++++-- kernel/sysctl.c | 7 ++ 6 files changed, 189 insertions(+), 7 deletions(-) -- 2.17.1
