On Wed, Sep 8, 2010 at 2:20 PM, Rayson Ho <rho@xxxxxxxxxx> wrote: > Hi all, > > I am a developer of Systemtap. I am looking into tracing KVM (the kernel > part and QEMU) and also the KVM guests with Systemtap. I googled and > found references to Xenprobes and xdt+dtrace, and I was wondering if > someone is working on the dynamic tracing interface for KVM? > > I've read the KVM kernel code and I think some expensive operations > (things that need to be trapped back to the host kernel - eg. loading of > control registers on x86/x64) can be interesting spots for adding an SDT > (static marker), and I/O operations performed for the guests can be > useful information to collect. > > I know that KVM guests run like a userspace process and thus techniques > for tracing Xen might be overkilled, and also gdb can be used to trace > KVM guests. However, are that anything special I need to be aware of > before I go further into the development of the Systemtap KVM probes? > > (Opinions / Suggestions / Criticisms welcome!) Hi Rayson, For the KVM kernel module Linux trace events are already used. For example, see arch/x86/kvm/trace.h and check out /sys/kernel/debug/tracing/events/kvm/*. There is a set of useful static trace points for vm_exit/vm_enter, pio, mmio, etc. For the KVM guest there is perf-kvm(1). This allows perf(1) to look up addresses inside the guest (kernel only?). It produces system-wide performance profiles including guests. Perhaps someone can comment on perf-kvm's full feature set and limitations? For QEMU userspace Prerna Saxena and I are proposing a static tracing patchset. It abstracts the trace backend (SystemTap, LTTng UST, DTrace, etc) from the actual tracepoints so that portability can be achieved. There is a built-in trace backend that has a basic feature set but isn't as fancy as SystemTap. I have implemented LTTng Userspace Tracer support, perhaps you'd like to add SystemTap/DTrace support with sdt.h? http://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg41323.html http://repo.or.cz/w/qemu/stefanha.git/shortlog/refs/heads/tracing_v3 Stefan -- 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
