From: Geert Uytterhoeven > Sent: 23 May 2023 08:30 > > 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. Hmmm.... tens of milliseconds is really much too long for RT threads. A limit nearer 1ms would be barely acceptable. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
