On 2011-05-12 11:33, Joerg Roedel wrote: > On Wed, May 11, 2011 at 11:55:28AM -0400, Avi Kivity wrote: >> This not-for-merging patchset exposes an emulated version 1 architectural >> performance monitoring unit to KVM guests. The PMU is emulated using >> perf_events, so the host kernel can multiplex host-wide, host-user, and the >> guest on available resources. >> >> Caveats: >> - counters that have PMI (interrupt) enabled stop counting after the >> interrupt is signalled. This is because we need one-shot samples >> that keep counting, which perf doesn't support yet >> - some combinations of INV and CMASK are not supported >> - counters keep on counting in the host as well as the guest >> - the RDPMC instruction and CR4.PCE bit are not yet emulated >> - there is likely a bug in the implementation; running 'perf top' in >> a guest that spends 80% of its time in userspace shows perf itself >> as consuming almost all cpu >> >> perf maintainers: please consider the first three patches for merging (the >> first two make sense even without the rest). If you're familiar with the Intel >> PMU, please review patch 5 as well - it effectively undoes all your work >> of abstracting the PMU into perf_events by unabstracting perf_events into what >> is hoped is a very similar PMU. > > Gaah, I was just about to submit a talk about PMU virtualization for KVM > Forum :) > > Anyway, I thought about a paravirt-approach instead of implementing a > real PMU... But there are certainly good reasons for both. Paravirt is taking away the pressure from CPU vendors to do their virt extensions properly - and doesn't help with unmodifiable OSes. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
