On Tue, Apr 05, 2022 at 02:15:51PM -0700, Guenter Roeck wrote: > Sebastian, > Hello Guenter, > On Tue, Apr 05, 2022 at 02:19:55PM +0000, Sebastian Ene wrote: > > This patch adds support for a virtual watchdog which relies on the > > per-cpu hrtimers to pet at regular intervals. > > > > The watchdog subsystem is not intended to detect soft and hard lockups. > It is intended to detect userspace issues. A watchdog driver requires > a userspace compinent which needs to ping the watchdog on a regular basis > to prevent timeouts (and watchdog drivers are supposed to use the > watchdog kernel API). > Thanks for getting back ! I wanted to create a mechanism to detect stalls on vCPUs and I am not sure if the current watchdog subsystem has a way to create per-CPU binded watchdogs (in the same way as Power PC has kernel/watchdog.c). The per-CPU watchdog is needed to account for time that the guest is not running(either scheduled out or waiting for an event) to prevent spurious reset events caused by the watchdog. > What you have here is a CPU stall detection mechanism, similar to the > existing soft/hard lockup detection mechanism. This code does not > belong into the watchdog subsystem; it is similar to the existing > hard/softlockup detection code (kernel/watchdog.c) and should reside > at the same location. > I agree that this doesn't belong to the watchdog subsytem but the current stall detection mechanism calls through MMIO into a virtual device 'qemu,virt-watchdog'. Calling a device from (kernel/watchdog.c) isn't something that we should avoid ? > Having said that, I could imagine a watchdog driver to be used in VMs, > but that would be similar to existing watchdog drivers. The easiest way > to get there would probably be to just instantiate one of the watchdog > devices already supported by qemu. > I am looking forward for your response, > Guenter Cheers, Sebastian
