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Re: [olpc-software] XRes Improvements



On Tue, Mar 14, 2006 at 04:42:00PM +0000, Matthew Allum wrote:
> Hi;
> 
> On Tue, 2006-03-14 at 16:04 +0000, Daniel P. Berrange wrote:
> > 
> > Absolutely this is useful :-) I've been working on this problem from a
> > completely different technical angle. I created an LD_PRELOAD hack
> > which intercepts the XCreatePixmap & XFreePixmap operations to log
> > the timing & all parameters of these two calls, and at time of XFreePixmap
> > call auto-dump it to a TIFF file. A little post-processing was used to
> > generate HTML pages display all pixmaps at specific points in time,
> > along with stack trace of the code allocating / freeing them.
> > 
> 
> Beware, tracking like that also, like regular XRes, suffers from
> ignoring window background pixmaps. I.e, code can do a;
> 
> pxm = XCreatePixmap(..)
> XSetWindowBackgroundPixmap(win, pxm)
> XFreePixmap(pxm);
> 
> But the pixmap is still allocated server side as the window background. 

Yeah, tracking that would require hooking in any methods relating to 
setting of window backgrouns, and also XDestroyWindow to track the 
implicit release I'd guess. For this use case, probably not worth the
effort in my LD_PRELOAD hack, but desirable for XRes to do this preperly

> > This extension to XRes is definitely a more pleasent way of capturing
> > the list of active pixmaps, since it doesn't require changing the way
> > an app runs before hand & thus much simpler for your typical user or 
> > developer to use.  
> 
> Another big advantage is you can run the test remotely with DISPLAY
> pointing at your target device. 
> 
> I am wondering if it would be practical to further extend XRes as to
> provide events when a client creates or frees a resource and avoid the
> need for any LD_PRELOAD-isms. 

The information I collect from the LD_PRELOAD is

  1. Width, height, depth
  2. Stack trace of caller for Create/Free
  3. Timestamp at which call occurred

An event when creating / deleting a pixmap would be sufficient to obtain
the timestamp, which is then used to correlate with specific actions 
performed from the Dogtail test script. So the only thing missing would 
then be the stack trace, which is a 'nice-to-have' but not really critical 
for high level analysis. 

BTW, I'll be posting the results of our tests & source code later today.

Regards,
Dan.
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