Messages in this thread | | | Date | Thu, 20 Aug 2009 18:53:44 +0200 | From | Martin Schwidefsky <> | Subject | Re: [circular locking bug] Re: [patch 00/15] clocksource / timekeeping rework V4 (resend V3 + bug fix) |
| |
On Thu, 20 Aug 2009 18:14:07 +0200 (CEST) Thomas Gleixner <tglx@linutronix.de> wrote:
> On Thu, 20 Aug 2009, Martin Schwidefsky wrote: > > On Thu, 20 Aug 2009 11:58:21 +0200 > > > There should be a time management kernel thread instead > > > (or workqueue), which does a proper state machine of all > > > these properties - without having to call this stuff from > > > within a timer handler. > > > > We could use that time managment kernel thread for the watchdog > > downgrade as well. Dunno if it is worth to create another kernel thread > > that just sits there doing nothing for 99.9% of the time. > > > > As for the fix: my brains starts to hurt looking at the pit clocksource > > code. Why does it set CLOCK_EVT_FEAT_ONESHOT but then unregisters the > > clocksource when the mode is set to CLOCK_EVT_MODE_ONESHOT?? That does > > not make any sense to me. I would have expected that the pit does not > > set CLOCK_EVT_MODE_ONESHOT. The timekeeping code wouldn't try use the > > clock for one-shot if the bit is not set. And to unregister the clock > > only because the mode is set to shutdown or unused doesn't seem to be > > necessary either. My fix would be to remove the CLOCK_EVT_MODE_ONESHOT > > bit from the features mask and to remove the clocksource_unregister > > from the set_mode callback. > > No. On UP machines we can run in oneshot mode with the PIT. > > The disable PIT clocksource hack was done in commit > 1a0c009ac53de4a7664a1239936f0bc258133156. Yes, in hindsight we should > have done 3f68535adad8dd89499505a65fb25d0e02d118cc in the first place. > > So now the simple and correct fix is to remove the unregister call.
Sorry if I don't see the obvious but how can that work? If the pit as clocksource is switched to CLOCK_EVT_MODE_ONESHOT it simply vanishes. How is it possible that a UP machine runs with the PIT in oneshot mode?
And yes, hindsight is easier than foresight.
-- blue skies, Martin.
"Reality continues to ruin my life." - Calvin.
| |