Re: [ltt-dev] LTTng-UST vs SystemTap userspace tracing benchmarks

[Julien Desfossez <julien dot desfossez at polymtl dot ca>]

On 02/15/2011 11:25 AM, William Cohen wrote:
> On 02/15/2011 10:53 AM, Julien Desfossez wrote:
>> LTTng-UST vs SystemTap userspace tracing benchmarks
>>
>> February 15th, 2011
>>
>> Authors: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
>>          Julien Desfossez <julien.desfossez@polymtl.ca>
> 
>> * SystemTap probe (stap testutrace.stp -F) :
>> probe process("./.libs/tracepoint_benchmark").mark("single_trace") {
>>     printf("%d : %s\n", gettimeofday_ns(), $arg1);
>> }

Hi William,
> How much of the SystemTap overhead is due to the printf() statement in the probe? What is the run time for the following:
> 
> probe process("./.libs/tracepoint_benchmark").mark("single_trace") {}
Except the fact that it produces a warning because the probe is empty,
the results differ a little but not as much as I expected. I also tested
(in flight recorder mode) with just removing the gettimeofday_ns() call
(and printing) :

# of threads   With printf    Without gtod_ns()   Without printf
1              0:58.36        0:52.27             0:46.45
2              1:49.94        1:37.61             1:27.33
4              2:38.49        2:35.13             2:50.87

> Is the code for the benchmarks available, so we can take a look at reducing the overhead of SystemTap?
For those who want to play with the benchmark, we setup a git repository
here : git://git.lttng.org/benchmarks.git

If you have any suggestions or ideas to make these tests better, we'll
be happy to integrate it.

Thanks,

Julien