Re: [Qemu-devel] [PATCH v2 3/3] trace: enable all events by default

[Stefan Hajnoczi <stefanha@gmail.com>]

On Wed, Nov 10, 2010 at 9:20 PM, Lluís <xscript@gmx.net> wrote:
> Blue Swirl writes:
>
>> On Wed, Nov 10, 2010 at 7:57 PM, Lluís <xscript@gmx.net> wrote:
>>> Blue Swirl writes:
>>>
>>>> On Wed, Nov 10, 2010 at 5:59 PM, Lluís <xscript@gmx.net> wrote:
>>>>> So, my patch is just a matter of having all events available _only_ when
>>>>> you use a backend other than "nop".
>>>
>>>> Then the default for simpletrace (and dtrace?) should also be disabled
>>>> initial state. If you have 1000 tracepoints automatically enabled at
>>>> start (with simpletrace, not nop), disabling all of them if you are
>>>> only interested in a few of them is difficult.
>>>
>>> That's how it is. The patch sets always ".state=0" in "simple", and
>>> "dtrace" just does not do anything unless you plug something into the
>>> probe (similarly with "ust").
>
>> Oh, I missed .state=0 part, it was also not mentioned in the
>> description. Then these changes should be OK.
>
> My fault. If these are to be merged I can cook up a new series with a
> more verbose description.

Jan Kiszka suggested a solution for the simple trace backend: have a
qemu -trace events=<file> command-line option that enables the trace
events listed in the file on startup.  Then we can really get rid of
disable.  On LTTng UST and SystemTap building with everything in is a
good default, the user must explicitly enable probes at runtime with
those trace backends anyway.

Currently .state = 0 makes the simple backend less usable since it's a
drag to manually enable trace events from the monitor every time.

Stefan