Re: [PATCH 3/5] trace: Add LTTng Userspace Tracer backend

[Jan Kiszka <jan.kiszka@web.de>]

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Stefan Hajnoczi wrote:
> This patch adds LTTng Userspace Tracer (UST) backend support.  The UST
> system requires no kernel support but libust and liburcu must be
> installed.
> 
> $ ./configure --trace-backend ust
> $ make
> 
> Start the UST daemon:
> $ ustd &
> 
> List available tracepoints and enable some:
> $ ustctl --list-markers $(pgrep qemu)
> [...]
> {PID: 5458, channel/marker: ust/paio_submit, state: 0, fmt: "acb %p
> opaque %p sector_num %lu nb_sectors %lu type %lu" 0x4b32ba}
> $ ustctl --enable-marker "ust/paio_submit" $(pgrep qemu)
> 
> Run the trace:
> $ ustctl --create-trace $(pgrep qemu)
> $ ustctl --start-trace $(pgrep qemu)
> [...]
> $ ustctl --stop-trace $(pgrep qemu)
> $ ustctl --destroy-trace $(pgrep qemu)
> 
> Trace results can be viewed using lttv-gui.
> 
> More information about UST:
> http://lttng.org/ust
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> ---
> I wrote this as part of trying out UST.  Although UST is promising, the
> usability is poor at the moment.

I was hoping it would be better, but I'm not really surprised.

> 
> The dependencies include the lttv trace viewer which I had to build from source
> (and it required a makefile tweak to build).  Luckily libust, liburcu, and
> ust-bin are packaged on my distro.
> 
> Error messages are periodically printed by the UST code when running QEMU.  I
> haven't investigated but this is may be due to signals interrupting UST's
> thread in poll().
> 
> Finally, the UST header files include some userspace ported kernel
> infrastructure and pollute the namespace.  I had to add some #undefs to get
> QEMU to build after including UST headers.
> 
> I don't see LTTng UST as a default option at the moment.  Hopefully this will
> change in the future.

Unless you already did, please report this to LTTng. I bet they will be
interested in your feedback and maybe also in the fact that they gained
another use/test case.

Jan



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