On Wed, May 11, 2011 at 03:58:34PM +0300, Avi Kivity wrote: > On 05/10/2011 06:04 PM, Roedel, Joerg wrote: >> On Tue, May 10, 2011 at 10:48:20AM -0400, Peter Zijlstra wrote: >> > On Tue, 2011-05-10 at 16:35 +0200, Joerg Roedel wrote: >> > > The AMD perf-counters support counting in guest or host-mode >> > > only. Make use of that feature when user-space specified >> > > guest/host-mode only counting. >> > >> > Subject mentions x86, does Intel have anything similar so you can make >> > it work for them too? >> >> Intel does not support guest or host-only counting in the hardware (at >> least according to my documentation). If wanted it could be approximated by >> enabling/disabling the counters in the guest-entry path. > > vmx has support for atomically swapping MSRs during guest entry and exit > (you can load guest MSRs on entry, save guest MSRs on exit, and load > host MSRs on exit, but you can't save host MSRs on entry, so host-only > counters cannot be 100% accurate). We'd need some kvm/perf hooks to > program these MSR swaps, and to manually save the counters that cannot > be done automatically. Well, wenn host counters are not saved on vmentry then we just need to save them manually (which is a one-time thing and does not need to happen at every vmentry). Thanks for that information, when I am back in office on monday I'll try to grab a machine and hopefully get this running. > btw, your patchset can be further improved by integrating > exclude_guest/exclude_host into the constraints. For example if we have > three general purpose counters, two generic perf_events in user, one > exclude_guest perf_event, and one exclude_host perf_event, we can > schedule them all at all times, swapping the exclude_guest and > exclude_host events during guest entry/exit. Well, it will need some additional code in the amd vmrun path too. I'll take a look at it, but probably leave it as a future optimization. Thanks for the hint. Joerg -- 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
