Jeremy Fitzhardinge wrote: > Prarit Bhargava wrote: > >> Jeremy Fitzhardinge wrote: >> >> >>> Prarit Bhargava wrote: >>> >>> >>> >>>> I'd like to see this patch implement/fix touch_cpu_softlockup_watchdog >>>> and touch_softlockup_watchdog to mimic touch_nmi_watchdog's behaviour. >>>> >>>> >>>> >>> Why? Is that more correct? It seems to me that you're interested in >>> whether a specific CPU has gone and locked up. If touching the watchdog >>> >>> makes it update all CPU timestamps, then you'll hide the fact that other >>> CPUs have locked up, won't it? >>> >>> >>> >>> >> In case of misuse, yes. But there are cases where we know that all CPUs >> will have softlockup issues, such as when doing a "big" sysrq-t dump. >> When doing the sysrq-t we take the tasklist_lock which prevents all >> other CPUs from scheduling -- this leads to bogus softlockup messages, >> so we need to reset everyone's watchdog just before releasing the >> tasklist_lock. >> >> Another question -- are you going to expose disable/enable_watchdog to >> other subsystems? Or are you going to expose touch_softlockup_watchdog? >> > > Well, it depends on who turns up. > > My first thought is to export both the global enable/disable interfaces > and touch_softlockup_watchdog. But on second thoughts maybe > touch_softlockup_watchdog is completely redundant, since you'd only do > IMO, if you export enable/disable you should drop touch_softlockup_watchdog. > it if you're holding off timer interrupts, but the lockup only gets > reported if timer interrupts are enabled (in other words, the best it > can tell you is "you locked up for a while there", which isn't terribly > useful). I like to think of the softlockup watchdog letting me know that a cpu hasn't scheduled in a long time. > So perhaps this can just be dropped. I haven't looked at the > users to see what they're really trying to achieve. > I've looked through much of that code for my previous patch ;) AFAICT the uses appear to be cases where we _know_ that we've gone away for a while and need to reset the timer. But there were some exceptions: touch_nmi_watchdog erroneously calls touch_softlockup_watchdog. In fact, touch_nmi_watchdog is trying to touch all cpus softlockup watchdogs, not just one. IIRC, There was an extra call to touch_softlockup_watchdog which wasn't necessary IIRC... Look at my previous patch where I replaced touch_softlockup_watchdog with touch_cpu_softlockup_watchdog ... > The enable/disable interfaces are more generally useful in that you can > say "I *know* I'm going to go away for a while, so don't bother > reporting it". > > J > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
