Hi Guenter, A few questions from an old discussion: On Mon, 8 Aug 2022 04:36:42 -0700, Guenter Roeck wrote: > On 8/5/22 15:07, Jean Delvare wrote: > > To be honest, I'm not sold to the idea of a software-emulated > > maximum timeout value above what the hardware can do, but if doing > > that makes sense in certain situations, then I believe it should be > > implemented as a boolean flag (named emulate_large_timeout, for > > example) to complement max_timeout instead of a separate time value. > > Is there a reason I'm missing, why it was not done that way? > > There are watchdogs with very low maximum timeout values, sometimes less than > 3 seconds. gpio-wdt is one example - some have a maximum value of 2.5 seconds. > rzn1_wd is even more extreme with a maximum of 1 second. With such low values, > accuracy is important, second-based limits are insufficient, and there is an > actual need for software timeout handling on top of hardware. Out of curiosity, what prevents user-space itself from pinging /dev/watchdog every 0.5 second? I assume hardware using such watchdog devices is "special" and would be running finely tuned user-space, so the process pinging /dev/watchdog could be given higher priority or even real-time status to ensure it runs without delays. Is that not sufficient? > At the same time, there is actually a need to make timeouts milli-second based > instead of second-based, for uses such as medical devices where timeouts need > to be short and accurate. The only reason for not implementing this is that > the proposals I have seen so far (including mine) were too messy for my liking, > and I never had the time to clean it up. Reverting milli-second support would > be the completely wrong direction. I might look into this at some point (for example as a SUSE Hackweek project). Did you post your work somewhere? I'd like to take a look. Thanks, -- Jean Delvare SUSE L3 Support
