* Avi Kivity <avi@xxxxxxxxxx> wrote: > On 03/16/2010 07:27 AM, Zhang, Yanmin wrote: > >From: Zhang, Yanmin<yanmin_zhang@xxxxxxxxxxxxxxx> > > > >Based on the discussion in KVM community, I worked out the patch to support > >perf to collect guest os statistics from host side. This patch is implemented > >with Ingo, Peter and some other guys' kind help. Yang Sheng pointed out a > >critical bug and provided good suggestions with other guys. I really appreciate > >their kind help. > > > >The patch adds new subcommand kvm to perf. > > > > perf kvm top > > perf kvm record > > perf kvm report > > perf kvm diff > > > >The new perf could profile guest os kernel except guest os user space, but it > >could summarize guest os user space utilization per guest os. > > > >Below are some examples. > >1) perf kvm top > >[root@lkp-ne01 norm]# perf kvm --host --guest --guestkallsyms=/home/ymzhang/guest/kallsyms > >--guestmodules=/home/ymzhang/guest/modules top > > > > Excellent, support for guest kernel != host kernel is critical (I > can't remember the last time I ran same kernels). > > How would we support multiple guests with different kernels? Perhaps a > symbol server that perf can connect to (and that would connect to guests in > turn)? The highest quality solution would be if KVM offered a 'guest extension' to the guest kernel's /proc/kallsyms that made it easy for user-space to get this information from an authorative source. That's the main reason why the host side /proc/kallsyms is so popular and so useful: while in theory it's mostly redundant information which can be gleaned from the System.map and other sources of symbol information, it's easily available and is _always_ trustable to come from the host kernel. Separate System.map's have a tendency to go out of sync (or go missing when a devel kernel gets rebuilt, or if a devel package is not installed), and server ports (be that a TCP port space server or an UDP port space mount-point) are both a configuration hassle and are not guest-transparent. So for instrumentation infrastructure (such as perf) we have a large and well founded preference for intrinsic, built-in, kernel-provided information: i.e. a largely 'built-in' and transparent mechanism to get to guest symbols. Thanks, Ingo -- 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
