Re: [Qemu-devel] [PATCH v2 1/1] monitor: improve tracing in handle_qmp_command

[Eric Blake]

On 07/28/2017 12:01 PM, Markus Armbruster wrote:
> "Denis V. Lunev" <address@hidden> writes:
> 
>> Calculate req_json only if trace_handle_qmp_command enabled.
>>
>> Signed-off-by: Denis V. Lunev <address@hidden>
>> CC: Stefan Hajnoczi <address@hidden>
>> CC: Lluís Vilanova <address@hidden>
>> CC: Dr. David Alan Gilbert <address@hidden>
>> CC: Markus Armbruster <address@hidden>
>> ---

> Conflicts with Eric's commit 8a4613a, but I can resolve that in my tree.
> 
> The commit message is too terse.  "Improve tracing" makes me think of
> more informative traces, but that's not the case.  What exactly is
> improved here?

Reduce overhead when not tracing.  Without the patch, we are malloc'ing
a QString and spending CPU cycles on converting a QObject to string,
just for the sake of sticking the string in the trace message - if we
aren't tracing, it's wasted effort.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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