On Wed, Jan 18, 2017 at 11:21:21AM +0000, Marc Zyngier wrote: > On 10/01/17 11:38, Punit Agrawal wrote: > > +#define VM_MASK GENMASK_ULL(31, 0) > > +#define EVENT_MASK GENMASK_ULL(32, 39) > > +#define EVENT_SHIFT (32) > > + > > +#define to_pid(cfg) ((cfg) & VM_MASK) > > +#define to_event(cfg) (((cfg) & EVENT_MASK) >> EVENT_SHIFT) > > + > > +PMU_FORMAT_ATTR(vm, "config:0-31"); > > +PMU_FORMAT_ATTR(event, "config:32-39"); > > I'm a bit confused by these. Can't you get the PID of the VM you're > tracing directly from perf, without having to encode things? And if you > can't, surely this should be a function of the size of pid_t? > > Mark, can you shine some light here? AFAICT, this is not necessary. The perf_event_open() syscall takes a PID separately from the perf_event_attr. i.e. we should be able to do: // monitor a particular vCPU perf_event_open(attr, vcpupid, -1, -1, 0) ... or .. // monitor a particular vCPU on a pCPU perf_event_open(attr, vcpupid, cpu, -1, 0) ... or ... // monitor all vCPUs on a pCPU perf_event_open(attr, -1, cpu, -1, 0) ... so this shouldn't be necessary. AFAICT, this is a SW PMU, so there should be no issue with using the perf_sw_context. If this is a bodge to avoid opening a perf_event per vCPU thread, then I completely disagree with the approach. This would be better handled in userspace by discovering the set of threads and opening events for each. Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
