Hi David, On Thu, May 11, 2023 at 12:49 PM David Laight <David.Laight@xxxxxxxxxx> wrote: > > * Geert Uytterhoeven <geert+renesas@xxxxxxxxx> [230510 13:23]: > > > It is considered good practice to call cpu_relax() in busy loops, see > > > Documentation/process/volatile-considered-harmful.rst. This can not > > > only lower CPU power consumption or yield to a hyperthreaded twin > > > processor, but also allows an architecture to mitigate hardware issues > > > (e.g. ARM Erratum 754327 for Cortex-A9 prior to r2p0) in the > > > architecture-specific cpu_relax() implementation. > > Don't you also need to call cond_resched() (at least some times). > Otherwise the process can't be pre-empted and a RT process > that last ran on that cpu will never be scheduled. According to [1], cond_resched() must be called at least once per few tens of milliseconds. read_poll_timeout() uses usleep_range(), which calls schedule_hrtimeout_range(). read_poll_timeout_atomic() should not be used with multi-ms timeouts anyway. So I guess we're OK? [1] https://elixir.bootlin.com/linux/latest/source/Documentation/RCU/Design/Requirements/Requirements.rst#L2348 Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
