Messages in this thread | | | Date | Wed, 10 May 2006 10:59:53 -0400 | From | Don Zickus <> | Subject | Re: [patch 8/8] Add abilty to enable/disable nmi watchdog from sysfs |
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On Wed, May 10, 2006 at 02:10:26AM -0700, Stephane Eranian wrote: > Don, > > Congratulations on the patch. I am glad to see that some of the SMP > issues I reported a long time ago are now fixed.
Thanks and glad I could help.
> > Adds a new /proc/sys/kernel/nmi call that will enable/disable the nmi > > watchdog. > > > > This means you can at runtime enable/disbale nmi_watchdog, i.e., reserve > some performance counters on the fly. This gets complicated because now > the perfmon subsystem (and probably oprofile) cannot check register > availability when they are first initialized. Basically each time, > the /sys entry is modified, they would have to scan the list of available > performance counters. I don't know exactly when Oprofile does this checking. > For perfmon, this is done only once, when the PMU description table is loaded. How often did you plan on enabling/disabling the nmi_watchdog? My understanding was you disable nmi_watchdog, run oprofile/perfmon, re-enable nmi_watchdog. I guess I don't understand what type of funky scenarios you are dealing with.
> > Also something that I did not see in this code is the error detection in > case enable_lapic_nmi_watchdog() fails. Oprofile runs on all CPUs or none. > Perfmon lets you monitor on subsets on CPUs. In case NMI was disabled and > a monitoring session was active on some CPUs. The enable_lapic_nmi_watchdog() > will fail on some CPUs. How is that handled?
It's not. In fact I wouldn't know what to do in such situations. Is it really wrong to only have a subset of cpus being monitored by the nmi_watchdog? This seems to be wandering into the area where the user is looking to do something complicated (profiling a subset of cpus) and as such might be expected to make sure the nmi_watchdog is properly enabled on all cpus when they are done.
Cheers, Don - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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