* Avi Kivity <avi@xxxxxxxxxx> wrote: > On 03/16/2010 11:53 AM, Ingo Molnar wrote: > >* Avi Kivity<avi@xxxxxxxxxx> wrote: > > > >>On 03/16/2010 09:24 AM, Ingo Molnar wrote: > >>>* 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. > >>The symbol server's client can certainly access the bits through vmchannel. > >Ok, that would work i suspect. > > > >Would be nice to have the symbol server in tools/perf/ and also make it easy > >to add it to the initrd via a .config switch or so. > > > >That would have basically all of the advantages of being built into the kernel > >(availability, configurability, transparency, hackability), while having all > >the advantages of a user-space approach as well (flexibility, extensibility, > >robustness, ease of maintenance, etc.). > > Note, I am not advocating building the vmchannel client into the host > kernel. [...] Neither am i. What i suggested was a user-space binary/executable built in tools/perf and put into the initrd. That approach has the advantages i listed above, without having the disadvantages of in-kernel code you listed. 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
