Re: [Qemu-devel] [PATCH 00/13] instrument: Add basic event instrumentation

From: "Lluís Vilanova" <vilanova@ac.upc.edu>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Daniel P. Berrange" <berrange@redhat.com>,
	Stefan Hajnoczi <stefanha@gmail.com>,
	"Emilio G. Cota" <cota@braap.org>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	QEMU Developers <qemu-devel@nongnu.org>
Subject: Re: [Qemu-devel] [PATCH 00/13] instrument: Add basic event instrumentation
Date: Thu, 27 Jul 2017 17:58:51 +0300	[thread overview]
Message-ID: <87lgnavsd0.fsf@frigg.lan> (raw)
In-Reply-To: <CAFEAcA8oyHi+7NVCE8YWHY+v0UXLbt2tWHGE4AP_V8TtDBc89g@mail.gmail.com> (Peter Maydell's message of "Thu, 27 Jul 2017 11:54:29 +0100")

Peter Maydell writes:

> On 27 July 2017 at 11:43, Daniel P. Berrange <berrange@redhat.com> wrote:
>> Maybe I'm missing something, but aren't all these things
>> already possible via either the statically defined tracepoints
>> QEMU exposes, or by placing dynamic tracepoints on arbitrary
>> code locations using dtrace/systemtap/lttng-ust.

> Last time I looked we didn't have tracepoints on most of
> the events you'd be interested in.

> That said, yes, I was going to ask if we could do this via
> leveraging the tracepoint infrastructure and whatever scripting
> facilities it provides. Are there any good worked examples of
> this sort of thing? Can you do it as an ordinary non-root user?

The hypertrace series I just sent contains an example that uses dtrace to
trigger changes on the tracing state of events based on information from other
events [1].

AFAIK it requires root privileges, and it's much less efficient than loading the
instrumentation library proposed in this series (see that there's also an API to
control event tracing).

[1] https://lists.gnu.org/archive/html/qemu-devel/2017-07/msg08458.html

Cheers,
  Lluis