On Fri, Aug 05, 2016 at 06:59:23PM +0200, Lluís Vilanova wrote:
> The hypertrace channel allows guest code to emit events in QEMU (the host) using
> its tracing infrastructure (see "docs/trace.txt"). This works in both 'system'
> and 'user' modes. That is, hypertrace is to tracing, what hypercalls are to
> system calls.
> 
> You can use this to emit an event on both guest and QEMU (host) traces to easily
> synchronize or correlate them. You could also modify you guest's tracing system
> to emit all events through the hypertrace channel, providing a unified and fully
> synchronized trace log. Another use case is timing the performance of guest code
> when optimizing TCG (QEMU traces have a timestamp).
> 
> See first commit for a full description.
> 
> Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
> ---

CCing Steven Rostedt, Masami Hiramatsu, Luiz Capitulino, and LTTng folks
who have all looked into host/guest tracing solutions.

Here is a mailing list archive link to this email thread:
https://lists.gnu.org/archive/html/qemu-devel/2016-08/msg01081.html

> 
> Lluís Vilanova (6):
>       hypertrace: Add documentation
>       hypertrace: Add tracing event "guest_hypertrace"
>       hypertrace: [*-user] Add QEMU-side proxy to "guest_hypertrace" event
>       hypertrace: [softmmu] Add QEMU-side proxy to "guest_hypertrace" event
>       hypertrace: Add guest-side user-level library
>       hypertrace: Add guest-side Linux module
> 
> 
>  Makefile                                           |    8 -
>  Makefile.objs                                      |    6 
>  bsd-user/main.c                                    |   16 +
>  bsd-user/mmap.c                                    |    2 
>  bsd-user/syscall.c                                 |    4 
>  configure                                          |   42 +++
>  docs/hypertrace.txt                                |  141 ++++++++++
>  docs/tracing.txt                                   |    3 
>  hypertrace/Makefile.objs                           |   20 +
>  hypertrace/guest/linux-module/Kbuild.in            |    5 
>  hypertrace/guest/linux-module/Makefile             |   24 ++
>  .../include/linux/qemu-hypertrace-internal.h       |   46 +++
>  .../linux-module/include/linux/qemu-hypertrace.h   |   71 +++++
>  hypertrace/guest/linux-module/qemu-hypertrace.c    |  133 +++++++++
>  hypertrace/guest/user/Makefile                     |   28 ++
>  hypertrace/guest/user/common.c                     |  221 +++++++++++++++
>  hypertrace/guest/user/qemu-hypertrace.h            |   77 +++++
>  hypertrace/softmmu.c                               |  243 +++++++++++++++++
>  hypertrace/user.c                                  |  292 ++++++++++++++++++++
>  hypertrace/user.h                                  |   52 ++++
>  include/hw/pci/pci.h                               |    2 
>  linux-user/main.c                                  |   19 +
>  linux-user/mmap.c                                  |    2 
>  linux-user/syscall.c                               |    3 
>  trace/Makefile.objs                                |    2 
>  25 files changed, 1460 insertions(+), 2 deletions(-)
>  create mode 100644 docs/hypertrace.txt
>  create mode 100644 hypertrace/Makefile.objs
>  create mode 100644 hypertrace/guest/linux-module/Kbuild.in
>  create mode 100644 hypertrace/guest/linux-module/Makefile
>  create mode 100644 hypertrace/guest/linux-module/include/linux/qemu-hypertrace-internal.h
>  create mode 100644 hypertrace/guest/linux-module/include/linux/qemu-hypertrace.h
>  create mode 100644 hypertrace/guest/linux-module/qemu-hypertrace.c
>  create mode 100644 hypertrace/guest/user/Makefile
>  create mode 100644 hypertrace/guest/user/common.c
>  create mode 100644 hypertrace/guest/user/qemu-hypertrace.h
>  create mode 100644 hypertrace/softmmu.c
>  create mode 100644 hypertrace/user.c
>  create mode 100644 hypertrace/user.h
> 
> 
> To: qemu-devel@nongnu.org
> Cc: Stefan Hajnoczi <stefanha@redhat.com>
>