Don, On Wed, May 10, 2006 at 10:59:53AM -0400, Don Zickus wrote: > > > > 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. > I thought that part of the exercise was to allow oprofile/perfmon and nmi_watchdog to work simultaneously, i.e., don't disable watchdog when you monitor. Leave watchdog on and have oprofile/perfmon run with fewer counters. The alternative would be to do what you say: disbale nmi, monitor, re-enable nmi. > > > > 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. > On larger machines (think NUMA-style), it does not always make sense to monitor all CPUs. -- -Stephane _______________________________________________ perfmon mailing list [email protected] http://www.hpl.hp.com/hosted/linux/mail-archives/perfmon/
