Mikael, On Tue, Jun 26, 2007 at 10:04:15AM +0200, Mikael Pettersson wrote: > On Mon, 25 Jun 2007 23:04:25 +0200, [EMAIL PROTECTED] wrote: > > > I think the tricky part is that we do want to reserve perfctr1 even > > > though the NMI watchdog is not active. This comes from the fact that > > > the NMI watchdog knows about only one counter and if it can't get that > > > one, it probably fails. By reserving it from the start, we ensure NMI > > > watchdog will work when eventually activated. > > > > Can you enable it later on at all? It failed for me when I tried, > > because it didn't know which hardware to use. Had to pass the kernel > > parameter to make the proc files do anything. Seems like it has to be > > enable at boot to work at all. > > > > And AFAICT we never unconditionally reserved a perfctr for the watchdog. > > Yes you can dynamically enable/disable the NMI watchdog, > at least if you booted with it enabled. > > > In 2.6.21 the nmi watchdog, if enabled, just reserved its perfctrs and > > everything else had to deal with it. Since the cleanup, the watchdog > > will release its perfctr when disabled, so another subsystem can grab > > it. But that also means that that other subsystem must release it again > > before you can reenable the watchdog. > > Which is the obvious and correct way to handle a shared resource. > Agreed.
> Keeping parts of the PMU HW permanently reserved whether or not > the watchdog is enabled would be a BUG. > True. But the upside is that you guarantee the activation of the NMI watchdog will always succeed which may be a valuable property given the goal of the NMI watchdog. Otherwise, if Oprofile or perfmon are active, the NMI will fail to grab a single counter. -- -Stephane - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
