Re: Tracing KVM with Systemtap

[Rayson Ho <rho@redhat.com>]

On Wed, 2010-09-08 at 15:08 +0100, Stefan Hajnoczi wrote:
> 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?

Thanks Stefan for the reply!

I've looked at the tracing additions in QEMU, including the "Simple
trace backend" (simpletrace.c) and the "tracetool" script, and I think
the SystemTap version can be implemented in a straightforward way.

One thing I was wondering, there seems to be not a lot of probes (except
the examples?) in the QEMU code, are we expected to see more probes in
the next release, or this work will be a long-term project that will not
be added to the official QEMU code in the near future?

(I believe if we can get the tracing framework integrated, then specific
probes can be added on-demand -- but of course that is just my own
opinion :-D )

Thanks,
Rayson




> 
> http://www.mail-archive.com/qemu-devel@nongnu.org/msg41323.html
> http://repo.or.cz/w/qemu/stefanha.git/shortlog/refs/heads/tracing_v3
> 
> Stefan
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