On 04/05/2012 03:37 PM, Gleb Natapov wrote: > On Thu, Apr 05, 2012 at 03:27:18PM +0300, Avi Kivity wrote: > > On 04/04/2012 01:29 PM, Gleb Natapov wrote: > > > > > > > > > ok. seems to be. will move over to perf as its working fine inside guest. > > > > > > > Good riddance IMO. I managed to run it on a guest (but not on my > > > host!). The thing is buggy. It does not use global ctrl MSR to enable > > > counters and kvm has all of them disabled by default. I didn't find what > > > value this MSR should have after reset, so this may be either kvm bug or > > > real BIOSes enable all counters in global ctrl MSR for PMUv1 > > > compatibility. Doing "wrmsr 0x38f 0x70000000f" solves this problem. The > > > second problem is that oprofile reprogram PMU counters without > > > disabling them first and this is explicitly prohibited by Intel SDM. > > > The patch below solve that, but oprofile is the one who should be fixed. > > > > Both should be fixed, there may be other profilers affected. > > > Global ctrl msr issue I need to investigate further, but second one is > bug that should be fixed in oprofile. Intel spec clearly says: > > EN (Enable Counters) Flag (bit 22) — When set, performance counting > is enabled in the corresponding performance-monitoring counter; when > clear, the corresponding counter is disabled. The event logic unit > for a UMASK must be disabled by setting IA32_PERFEVTSELx[bit 22] = 0, > before writing to IA32_PMCx. > > I suspect that on real HW they got wrong result too. It simply subtly > wrong, so it is not as noticeable as with kvm. > First, there is the standard Linus rant to never break userspace (and for us a guest kernel is userspace). Second, the Intel rule may have been added later (as preparation for a change in behaviour), so it may actually work correctly on older hardware. -- error compiling committee.c: too many arguments to function -- 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
