On 28.03.2022 12:05:57, Sebastian Andrzej Siewior wrote: > On 2022-03-23 15:55:58 [+0100], Rasmus Villemoes wrote: > > This RFC is motivated by an old problem in the tty layer. Ever since > > commit a9c3f68f3cd8 (tty: Fix low_latency BUG), use of UART for > > real-time applications has been problematic. Even if both the > > application itself and the irq thread are set to SCHED_FIFO, the fact > > that the flush_to_ldisc work is scheduled on the generic and global > > system_unbound_wq (with all workers running at normal scheduling > > priority) means that UART RX can suffer unbounded latency. > > Having a kthread per "low-latency" tty instance is something I would > prefer. The kwork corner is an anonymous worker instance and probably > does more harm than good. Especially if it is a knob for everyone which > is used for the wrong reasons and manages to be harmful in the end. > With a special kthread for a particular tty, the thread can be assigned > with the desired priority within the system and ttyS1 can be > distinguished from ttyS0 (and so on). This turned out to be useful in a > few setups over the years. +1 The networking subsystem has gone the same/similar way with NAPI. NAPI handling can be switched from the softirq to kernel thread on a per interface basis. regards Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung West/Dortmund | Phone: +49-231-2826-924 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
Attachment:
signature.asc
Description: PGP signature
