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2022-05-18realtime: request SCHED_RR using CAP_SYS_NICERouven Czerwinski
Try to gain SCHED_RR (round-robin) realtime scheduling privileges before starting the server. This requires CAP_SYS_NICE on Linux systems. We additionally register a pthread_atfork callback which resets the scheduling class back to SCHED_OTHER (the Linux system default). Due to CAP_SYS_NICE, setting RLIMIT_RTPRIO has no effect on the process as documented within man 7 sched (from Linux): Privileged (CAP_SYS_NICE) threads ignore the RLIMIT_RTPRIO limit; as with older kernels, they can make arbitrary changes to scheduling policy and priority. See getrlimit(2) for further information on RLIMIT_RTPRIO Note that this requires the sway distribution packagers to set the CAP_SYS_NICE capability on the sway binary. Supersedes #6992