jschoubben
8f7db549ae
The walk for setuid programs is put in the idle I/O class so it yields to everything else, but only a scheduler that schedules by class (BFQ) honours that. The control-node's disks run mq-deadline, which does not, so the walk read at full priority. On 2026-10-11 the walk started at 01:27, right after the engine applied a new controller, and ran sixteen minutes; it kept two spinning disks saturated, the bus whose store shares them stalled for half a minute twice, and the controller lost its lease and restarted each time. The walk now also paces itself by PSI, which reads the same whatever the scheduler: before it reads a directory, while some task has waited on I/O for more than 10 % of the last ten seconds, it pauses two seconds at a time. It looks at most every 250 ms, pauses at most 30 s in a row and then reads one more directory, so a machine that is never quiet is walked slowly but still judged. Its own reads count in the pressure, so on an otherwise idle machine it holds the disk below the bound. Pressure it cannot read pauses nothing, and is said once. A paced walk finds what an unpaced one finds; a walk ended while it pauses is an incomplete walk, never one that found nothing.