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 _______________________________________________ perfmon mailing list [email protected] http://www.hpl.hp.com/hosted/linux/mail-archives/perfmon/
