[cairo] Performance analysis of a Cairo application

[Jeff Muizelaar]

On Fri, Oct 19, 2007 at 02:42:51PM -0400, Jeff Muizelaar wrote:
> On Fri, Oct 19, 2007 at 04:18:12PM -0200, Ivan Baldo wrote:
> >    Hello Dan, thanks for answering!
> > 
> > 
> > El 18/10/07 19:38, Dan Amelang escribió:
> > >On 10/17/07, Ivan Baldo <ibaldo at adinet.com.uy> wrote:
> > >  
> > >>    Hello.
> > >>    I want my (under development) application to run faster, so I want
> > >>to know where most of the time is spent to focus this optimization effort.
> > >>...
> > >>    Instead I am getting things like this:
> > >>    1% main()
> > >>99% draw()
> > >>    50% drawThings1()
> > >>    50% drawThings2()
> > >>    Thats because both functions have equal complexity on my code, but I
> > >>know that actually drawThings1 is using Cairo in a way that it is slower
> > >>for Cairo or my graphics card to process than drawThings2.
> > >>    
> > >
> > >And how do you know this?
> > >  
> >    Intuition, and I know that it isn't the right way to profile 
> > programs and optimize them, thats why I looked at gprof and oprofile, 
> > but didn't get meaningful results for my purpose, so after googling a 
> > bit I decided that it was time to ask for help :-).
> > 
> > 
> > >The Right Thing To Do is use oprofile to get global, system-wide
> > >profiles what will contain performance information for both your
> > >application code, cairo, and the X server. That should be all you
> > >need, don't worry about the work your graphics card is doing. It's
> > >unlikely that your graphics card is involved in the bottleneck, in
> > >fact, on many (most?) systems today, the graphics card isn't doing
> > >that much to accelerate cairo (yet).
> > >
> > >So you want to find out what your CPU is spending its time doing, and
> > >oprofile is the way to get that.
> > >  
> >    I get that with oprofile, you are right, but it is not what I am 
> > looking because it is not centered on _the outside effects accumulated 
> > on my application_.
> >    Maybe I am not being clear by email (or my bad English), to help 
> > explain this a bit (and to simplify my research) I made this simple 
> > standalone Cairo XRender application (based on the Cairo boilerplate 
> > code) that it is attached.
> >    It has two functions (testfast and testslow) that call one function 
> > that does the actual work but only varying the size of the drawing.
> >    I get this output:
> > Elapsed times: fast 3710ms (22%), slow 12892ms (77%), total 16602ms.
> >    It doesn't matter if I use gprof or qprof or oprofile, none of this 
> > tools told me that testfast accumulated to the 22% of the running time 
> > and that testslow accumulated to the 77% of the running time.
> >    To repeat, I would like a call-graph that says something like this:
> > 
> > main
> >    77% testslow
> >        77% test
> >    22% testfast
> >        22% test
> > 
> > testslow
> >    100% test
> > 
> > testfast
> >    100% test
> 
> Sysprof can do this. The important point here is that you want to record
> an entire backtrace at each sampling point instead of just the program
> counter. I'm not sure whether gprof, qprof, or oprofile support
> capturing an entire backtrace, but sysprof certainly does.
> 
> However, because you are using X and that is where the majority of the
> cpu time is being spent. Sysprof will not be able to associate the time
> spent in X with the calling function (testfast or testslow) because the
> backtraces stay inside each process.

It may also be possible to do single process profiling where time
sleeping gets accounted to the function that caused the sleeping.
However, I don't know of any tools that do this. (There might be some, I
haven't really ever looked...)

One possible way of doing this would be to use setitimer with
ITIMER_REAL instead of ITIMER_PROF which is what I expect qprof uses.

-Jeff